You could add a property to your form, say icSiteFilter, and set that in THISFORM.INIT(). Then:

WITH THISFORM
.oQuery.SHOW()

lcFilter = .icSiteFilter

IF !EMPTY( .oQuery.cFilter )
lcFilter + " AND " + .oQuery.cFilter
ENDIF

SET FILTER TO &lcFilter

.REFRESH()
ENDWITH

>On my form, I have "Set Filter" button that has the following code:
>
>with thisform
> .oQuery.show()
> lcFilter=.oQuery.cFilter
> set filter to &lcFilter
> .refresh()
>endwith
>
>The DE for this form has a table that has a filter always set based on the site the user choose when opening the application. Ex. Inventory.SiteID==gnSiteID.
>
>How can I append the current filter to the filer statement returned form oQuery?
>
>Thanks
>Kirk