In chemotherapy, the problem of finding the right drug for the right patient is based upon the premise that drugs have specific actions and that a particular agent may be beneficial for certain patients but not for others. The drug of choice in this study was defined in terms of the best prediction from multiple regression equations developed on groups that had received 3 different tranquilizing drugs, using pretreatment symptomatology as the predictors. Cross-validation of these assignments on an independent sample confirmed the hypothesis that patients respond best if assigned to their drug of choice. Simple random assignment of patients to the different drugs would have led to an acceptance of the null hypothesis. (21 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)