1. One hundred and eighty voluntary inpatients (102 schizophrenic subjects, 67 subjects with affective disorders, and 11 "other" diagnoses) were studied during treatment with imipramine.2. Seven imipramine induced behavioral reaction patterns and their relationships to diagnosis, age, sex, patterns of medication use, and hospital discharge evaluation are presented. These include mood elevation, explicit verbal denial, manic, reduction of episodic anxiety, agitated disorganization, anhedonic socialization, and non-response.3. Imipramine was favorably evaluated in 79% of subjects with affective disorders and 51% of schizophrenic patients.4. The use of psychiatric reaction patterns to psychotropic drugs for categorizing patients and providing a basis for a more rational pharmacotherapy are emphasized.