In the area of clinical inquiry, knowledge takes its character from its specific sources. This sobering truism is perhaps never more obvious than when investigators attempt to identify those individual differences which precede and, hopefully, might be used to anticipate individual differences in therapeutic response. At the Annual Meeting of the American College of Neuropsychopharmacology, the predictive use of pretreatment considerations served as an integrating theme for several reports of ongoing clinical investigation. Because of their common focus, these papers are presented in two consecutive issues of theJournal.