Where do you put this code, in which Event?
I suggestion to assign properties in windows property because of you may put code miss Event,that code may not work.
such as :
in property window of combobox1 assign :
RowSourceType = 3
RowSource=SELECT FIELDNAME FROM TABLENAME WHERE FIELDNAME = MYVALUE INTO CURSOR MYCURSOR
ColumnCount = 1

*MYVALUE you must set PUBLIC variable or You may add new form Property instead of variable myvalue (ThisForm.myValue)

and then you put code into GotFocus Event of Combobox1
This.Requery()

icq# 74778615