I think you need the &lcWhere and your Case looks a bit odd to me. Try

LOCAL lcwhere1
SET EXCLUSIVE OFF
SET DELETED ON

DO CASE
	CASE thisform.combo1.displayvalue='='
           lcwhere="modacad.key3=thisform.combo1.displayvalue"
	CASE thisform.combo1.displayvalue='=='
           lcwhere="modacad.key3==thisform.combo1.displayvalue"
	CASE thisform.combo1.displayvalue='$'
           lcwhere="modacad.key3$thisform.combo1.displayvalue"
ENDCASE
SELECT * ;
FROM ("U:\Data\modacad.dbf") ;
WHERE &lcwhere ;
order BY mainkey ;
INTO CURSOR crssearch

>Thanks Caroline,
>
>I decided to use variables in a case statements:
>
>

>LOCAL lcwhere1, lcwhere2, lcwhere3
>SET EXCLUSIVE OFF
>SET DELETED ON
>
>lcwhere1="modacad.key3=thisform.combo1.displayvalue"
>lcwhere2="modacad.key3==thisform.combo1.displayvalue"
>lcwhere3="modacad.key3$thisform.combo1.displayvalue"
>
>DO CASE
>	CASE 1
>		IF thisform.combo1.displayvalue='='
>			SELECT * ;
>			FROM ("U:\Data\modacad.dbf") ;
>			WHERE lcwhere1 ;
>			order BY mainkey ;
>			INTO CURSOR crssearch
>		ENDIF
>	CASE 2
>		IF thisform.combo1.displayvalue='=='
>			SELECT * ;
>			FROM ("U:\Data\modacad.dbf") ;
>			WHERE lcwhere2 ;
>			order BY mainkey ;
>			INTO CURSOR crssearch
>		ENDIF
>	CASE 3
>		IF thisform.combo1.displayvalue='$'
>			SELECT * ;
>			FROM ("U:\Data\modacad.dbf") ;
>			WHERE lcwhere3 ;
>			order BY mainkey ;
>			INTO CURSOR crssearch
>		ENDIF
>
>ENDCASE
>

>
>I get a syntax error. Do you have any ideas as to why this doesn't work?
>
>Thanks Caroline