Thanks Herman, your code is great. Portions of it are exactly what I was working on. However, I cannot use the HIDd api because the USB device I am working with is NOT a true human interface device standard and doesn't respond to the HIDd api calls, but can be accessed directly via USB. I started out a month ago using the HIDd api until I found out the device does not list itself as HID device, but only a USB Printer which can be written to and read from (it contains a card reader). I tested your code using either the PRINTER GUID or the HARD DRIVE GUID and neither return any information (except if I pass it a HID Guid then it does return information on my MSFT Keyboard which is indeed a true HID device):

#Define MAX_PATH                260
#Define ERROR_NO_MORE_ITEMS     259
#Define INVALID_HANDLE_VALUE    -1
#Define DIGCF_DEVICEINTERFACE   0x0010
#Define DIGCF_PRESENT           0x0002

#Define GUID_Size  16
#Define SP_DEVICE_INTERFACE_DATA_Size  28
#Define SP_DEVICE_INTERFACE_DETAIL_DATA_Size  5

Local ls_GUID, lh_DevInfo

Declare Long GetLastError in Kernel32
Declare Long CloseHandle in Kernel32 Long hObject
Declare Long CreateFile in Kernel32 ;
   String cFileName, Long dwDesiredAccess, Long dwShareMode, ;
   String @ lpSecurityAttributes, Long dwCreationDisposition, ;
   Long dwFlagsAndAttributes, Long hTemplateFile

Declare HidD_GetHidGuid in HID ;
   String @ O_sHidGuid

Declare Long HidD_GetProductString in HID ;
   Long hHidDeviceObject, String @ O_cBuffer, Long nBufferLength

Declare Long SetupDiDestroyDeviceInfoList in SetupAPI ;
   Long hDeviceInfoSet

Declare Long SetupDiGetClassDevs in SetupAPI ;
   String @ sGUID, String Enumerator, Long nhWnd, Long nFlags

Declare Long SetupDiEnumDeviceInterfaces in SetupAPI ;
   Long hDeviceInfo, String @ sDeviceInfoData, ;
   String @ sInterfaceClassGuid, Long MemberIndex, ;
   String @ O_sDeviceInterfaceData

Declare Long SetupDiGetDeviceInterfaceDetail in SetupAPI ;
   Long hDeviceInfo, String @ sDeviceInterfaceData, ;
   String @ O_sDeviceInterfaceDetailData, Long DeviceInterfaceDetailDataSize, ;
   Long @ O_nRequiredSize, String @ O_sDeviceInfoData


****************************************
** Main

ls_HidGuid = space( GUID_Size )
HidD_GetHidGuid( @ls_HidGuid )
#DEFINE GUID_DEVCLASS_PRINTER ;
	CHR(0x4D) + CHR(0x36) + CHR(0xE9) + CHR(0x79) + ;
	CHR(0xE3) + CHR(0x25) + CHR(0x11) + CHR(0xCE) + ;
	CHR(0xBF) + CHR(0xC1) + CHR(0x08) + CHR(0x00) + ;
	CHR(0x2B) + CHR(0xE1) + CHR(0x03) + CHR(0x18)
#Define GUID_DEVCLASS_DISKDRIVE ;
	Chr(0x67) + Chr(0xE9) + Chr(0x36) + Chr(0x4D) + ;
	Chr(0x25) + Chr(0xE3) + ;
	Chr(0xCE) + Chr(0x11) + ;
	Chr(0xBF) + Chr(0xC1) + Chr(0x08) + Chr(0x00) + Chr(0x2B) + Chr(0xE1) + Chr(0x03) + Chr(0x18)

ls_hidGuid = GUID_DEVCLASS_DISKDRIVE

If !empty( ls_HidGuid )
   lh_DevInfo = SetupDiGetClassDevs( ls_HidGuid, 0, 0, ;
      DIGCF_PRESENT + DIGCF_DEVICEINTERFACE )

   If (lh_DevInfo != INVALID_HANDLE_VALUE)
      Clear
      EnumerateDevices( lh_DevInfo, ls_HidGuid )
      SetupDiDestroyDeviceInfoList( lh_DevInfo )
   endif
endif

* Clear Dlls


****************************************
** Procedures

Procedure EnumerateDevices( th_DevInfo, ts_Guid )
   Local ls_DiData, ls_DiDetailData, lh_Device
   Local ln_Error, ln_Index, ln_ReqSize
   Local lc_DeviceName, lw_Buffer, lc_Buffer

   Store 0 to ln_Error, ln_Index, ln_ReqSize
   ls_DiData = padr( BinToC( SP_DEVICE_INTERFACE_DATA_Size, '4rs' ), ;
      SP_DEVICE_INTERFACE_DATA_Size, chr(0) )

   Do while (ln_Error != ERROR_NO_MORE_ITEMS)
      If (SetupDiEnumDeviceInterfaces( th_DevInfo, 0, ts_Guid, ln_Index, @ls_DiData ) == 0)
         ln_Error = GetLastError()
         If (ln_Error != ERROR_NO_MORE_ITEMS)
            ShowError( ln_Error, ln_Index, 'SetupDiEnumDeviceInterfaces()' )
         ELSE
         	? [ No More Devices]
         endif
      else

         SetupDiGetDeviceInterfaceDetail( th_DevInfo, ls_DiData, ;
            0, 0, @ln_ReqSize, 0 )
         ls_DiDetailData = padr( BinToC( SP_DEVICE_INTERFACE_DETAIL_DATA_Size, '4rs' ), ;
            ln_ReqSize, chr(0) )
         ln_Result = SetupDiGetDeviceInterfaceDetail( th_DevInfo, ls_DiData, ;
            @ls_DiDetailData, ln_ReqSize, @ln_ReqSize, 0 )

         If (ln_Result == 1)
            lc_DeviceName = substr( ls_DiDetailData, 5 )
            ln_Pos = at( chr(0), lc_DeviceName )
            If (ln_Pos > 0)
               lc_DeviceName = left( lc_DeviceName, ln_Pos - 1 )
            endif
?lc_DeviceName
            lh_Device = CreateFile( lc_DeviceName, 0x80000000, 0x1, 0, 3, 0x20000000, 0 )
            If (lh_Device != INVALID_HANDLE_VALUE)
               lw_Buffer = space( MAX_PATH )
               If (HidD_GetProductString( lh_Device, @lw_Buffer, MAX_PATH ) == 1)
                  lc_Buffer = MakeANSI( lw_Buffer )
                  ? 'Product Name: ' + lc_Buffer
               endif
               CloseHandle( lh_Device )
            else
               ShowError( GetLastError(), ln_Index, 'CreateFile()' )
            endif
         else
            ShowError( GetLastError(), ln_Index, 'SetupDiGetDeviceInterfaceDetail()' )
         endif
         ln_Index = ln_Index + 1
      endif
   enddo
EndProc


Procedure ShowError( tn_Error, tn_Index, tc_Message )
   ? tc_Message + ' ERROR !!'
   If (VarType( tn_Index ) == 'N')
      ? 'Member index:', tn_Index
   endif
   ? 'Error No:', tn_Error
EndProc


Procedure MakeANSI( tw_String )
   Local lc_String, ln_Pos

   lc_String = strconv( strconv( tw_String, 6 ), 2 )
   ln_Pos = at( chr(0), lc_String )
   If (ln_Pos > 0)
      lc_String = left( lc_String, ln_Pos - 1 )
   endif

   Return lc_String
EndProc

>>I looked at that and was sure that I added the size up correctly. Just goes to show you! Thanks Herman. However, I wonder why it is returning No more Devices (259)? the guid I'm passing is for the hard drive, and it works if I check the registry. Can you run this code and let me know what it returns for you?
>
>It returns the same for me (no more devices). I have a question, where did you get the GUID_DEVCLASS_DISKDRIVE? Also, I tried to run the commented part, all returns ERROR
>
>This code works for me to enumerate the USB Devices, try this:
>

>#Define MAX_PATH                260
>#Define ERROR_NO_MORE_ITEMS     259
>#Define INVALID_HANDLE_VALUE    -1
>#Define DIGCF_DEVICEINTERFACE   0x0010
>#Define DIGCF_PRESENT           0x0002
>
>#Define GUID_Size  16
>#Define SP_DEVICE_INTERFACE_DATA_Size  28
>#Define SP_DEVICE_INTERFACE_DETAIL_DATA_Size  5
>
>Local ls_GUID, lh_DevInfo
>
>Declare Long GetLastError in Kernel32
>Declare Long CloseHandle in Kernel32 Long hObject
>Declare Long CreateFile in Kernel32 ;
>   String cFileName, Long dwDesiredAccess, Long dwShareMode, ;
>   String @ lpSecurityAttributes, Long dwCreationDisposition, ;
>   Long dwFlagsAndAttributes, Long hTemplateFile
>
>Declare HidD_GetHidGuid in HID ;
>   String @ O_sHidGuid
>
>Declare Long HidD_GetProductString in HID ;
>   Long hHidDeviceObject, String @ O_cBuffer, Long nBufferLength
>
>Declare Long SetupDiDestroyDeviceInfoList in SetupAPI ;
>   Long hDeviceInfoSet
>
>Declare Long SetupDiGetClassDevs in SetupAPI ;
>   String @ sGUID, String Enumerator, Long nhWnd, Long nFlags
>
>Declare Long SetupDiEnumDeviceInterfaces in SetupAPI ;
>   Long hDeviceInfo, String @ sDeviceInfoData, ;
>   String @ sInterfaceClassGuid, Long MemberIndex, ;
>   String @ O_sDeviceInterfaceData
>
>Declare Long SetupDiGetDeviceInterfaceDetail in SetupAPI ;
>   Long hDeviceInfo, String @ sDeviceInterfaceData, ;
>   String @ O_sDeviceInterfaceDetailData, Long DeviceInterfaceDetailDataSize, ;
>   Long @ O_nRequiredSize, String @ O_sDeviceInfoData
>
>
>****************************************
>** Main
>
>ls_HidGuid = space( GUID_Size )
>HidD_GetHidGuid( @ls_HidGuid )
>If !empty( ls_HidGuid )
>   lh_DevInfo = SetupDiGetClassDevs( ls_HidGuid, 0, 0, ;
>      DIGCF_PRESENT + DIGCF_DEVICEINTERFACE )
>
>   If (lh_DevInfo != INVALID_HANDLE_VALUE)
>      Clear
>      EnumerateDevices( lh_DevInfo, ls_HidGuid )
>      SetupDiDestroyDeviceInfoList( lh_DevInfo )
>   endif
>endif
>
>* Clear Dlls
>
>
>****************************************
>** Procedures
>
>Procedure EnumerateDevices( th_DevInfo, ts_Guid )
>   Local ls_DiData, ls_DiDetailData, lh_Device
>   Local ln_Error, ln_Index, ln_ReqSize
>   Local lc_DeviceName, lw_Buffer, lc_Buffer
>
>   Store 0 to ln_Error, ln_Index, ln_ReqSize
>   ls_DiData = padr( BinToC( SP_DEVICE_INTERFACE_DATA_Size, '4rs' ), ;
>      SP_DEVICE_INTERFACE_DATA_Size, chr(0) )
>
>   Do while (ln_Error != ERROR_NO_MORE_ITEMS)
>      If (SetupDiEnumDeviceInterfaces( th_DevInfo, 0, ts_Guid, ln_Index, @ls_DiData ) == 0)
>         ln_Error = GetLastError()
>         If (ln_Error != ERROR_NO_MORE_ITEMS)
>            ShowError( ln_Error, ln_Index, 'SetupDiEnumDeviceInterfaces()' )
>         endif
>      else
>
>         SetupDiGetDeviceInterfaceDetail( th_DevInfo, ls_DiData, ;
>            0, 0, @ln_ReqSize, 0 )
>         ls_DiDetailData = padr( BinToC( SP_DEVICE_INTERFACE_DETAIL_DATA_Size, '4rs' ), ;
>            ln_ReqSize, chr(0) )
>         ln_Result = SetupDiGetDeviceInterfaceDetail( th_DevInfo, ls_DiData, ;
>            @ls_DiDetailData, ln_ReqSize, @ln_ReqSize, 0 )
>
>         If (ln_Result == 1)
>            lc_DeviceName = substr( ls_DiDetailData, 5 )
>            ln_Pos = at( chr(0), lc_DeviceName )
>            If (ln_Pos > 0)
>               lc_DeviceName = left( lc_DeviceName, ln_Pos - 1 )
>            endif
>
>            lh_Device = CreateFile( lc_DeviceName, 0x80000000, 0x1, 0, 3, 0x20000000, 0 )
>            If (lh_Device != INVALID_HANDLE_VALUE)
>               lw_Buffer = space( MAX_PATH )
>               If (HidD_GetProductString( lh_Device, @lw_Buffer, MAX_PATH ) == 1)
>                  lc_Buffer = MakeANSI( lw_Buffer )
>                  ? 'Product Name: ' + lc_Buffer
>               endif
>               CloseHandle( lh_Device )
>            else
>               ShowError( GetLastError(), ln_Index, 'CreateFile()' )
>            endif
>         else
>            ShowError( GetLastError(), ln_Index, 'SetupDiGetDeviceInterfaceDetail()' )
>         endif
>         ln_Index = ln_Index + 1
>      endif
>   enddo
>EndProc
>
>
>Procedure ShowError( tn_Error, tn_Index, tc_Message )
>   ? tc_Message + ' ERROR !!'
>   If (VarType( tn_Index ) == 'N')
>      ? 'Member index:', tn_Index
>   endif
>   ? 'Error No:', tn_Error
>EndProc
>
>
>Procedure MakeANSI( tw_String )
>   Local lc_String, ln_Pos
>
>   lc_String = strconv( strconv( tw_String, 6 ), 2 )
>   ln_Pos = at( chr(0), lc_String )
>   If (ln_Pos > 0)
>      lc_String = left( lc_String, ln_Pos - 1 )
>   endif
>
>   Return lc_String
>EndProc
>