Effects of intravenous chlordiazepoxide at three dose levels (0.5 mg. per kilogram, 1.0 mg. per kilogram, and 1.5 mg. per kilogram) were studied in 7 conscious volunteers. Meperidine (0.5 mg. per kilogram), pentobarbital sodium (1.0 mg. per kilogram), promethazine (0.5 mg. per kilogram), and a placebo were included for comparison in the study. Evaluation of responses in the postinjection period indicated that (1) promethazine caused the most severe subjective effects, (2) subjects receiving 1.0 mg. per kilogram of chlordiazepoxide appeared to behave as though they had received meperidine or pentobarbital, and (3) there was rw hypotension even at the highest dose level of chlordiazepoxide.