In their letter, McLaughlin and Tso have misinterpreted the purpose of the short-term diagnostic drug trial we have proposed (Pediatrics 61:21, 1978). We developed our laboratory test procedure to screen out potential adverse responders, in order to prevent their mistreatment with stimulant drugs. We feel that this conservative bias is necessary, since there has been general agreement since Bradley's (1939, 1950) initial work that not all behaviorally hyperactive children have a favorable response to stimulant drug.1,2