You should also consider:

IF  TYPE("loMyObject." + cNewProperty) = "U"
   ADDPROPERTY(loMyObject,cNewProperty,"Test Value")
ENDIF

If you know the name of the property and it's not a variable you can also use VARTYPE() for better performance yet:

IF  TYPE(loObject.cProperty) = "U"
   ADDPROPERTY(loMyObject,"cProperty","Test Value")
ENDIF

I suspect either of these will be faster faster than either PEMSTAUS and certainly AMEMBERS.

+++ Rick ---

>I have a program that checks to see if a property already exists on an object before adding it, which would be the better way to determine if the property already exists?
>
>

>    AMEMBERS( m.laPropertySet, m.loMyObject )
>    IF ASCAN(m.laPropertySet,[cNewProperty],1,0,1,1)>0 && Case insensitive search, 0-not found
>      ADDPROPERTY( m.loMyObject, [cNewProperty], [Test Information])
>    ENDIF
>    
>    && or should I do this instead:
>    
>    IF PEMSTATUS( m.loMyObject, [cNewProperty], 5)
>      ADDPROPERTY( m.loMyObject, [cNewProperty], [Test Information])
>    ENDIF
>

>
>What do you think?