1. Diazepam in high doses, up to 400 mg per day, was administered to paranoid schizophrenic patients in a double-blind placebo-controlled study. 2. The effects of treatment were assessed by the following: the Brief Psychiatric Rating Scale (BPRS); the Clinical Global Impressions Scale (CGI); the Schizophrenia Subscale of the Present State Examination (SS-PSE); the Simpson-Angus Rating Scale (SARS) for extrapyramidal symptoms; the Nurses' Observation Scale for Inpatient Evaluation (NOSIE); and a 90 item Self-Assessment Questionnaire (SCL-90). 3. Within a few hours to a few days from the onset of diazepam treatment both positive (such as auditory hallucinations and persecutory delusions) and negative (such as emotional withdrawal and blunted affect) schizophrenic symptoms were dramatically eliminated in 5 out of the 6 patients.