A survey of 133 senior medical students revealed that noteworthy proportions had used the following psychoactive substances during their lifetime: cigarettes, 44%; alcohol, 96%; marijuana, 57%; amphetamines, 22%; cocaine, 20%; sedatives, 17%; benzodiazepines, 37%; hallucinogens, 15%; and opioids, 40%. Smaller percentages reported use of these substances during the last year and the last month. Lifetime use did not vary significantly by sex, ethnic status, or marital status. Twelve percent reported nearly daily use of one or more substances during the last month; a different but overlapping 11% reported substance abuse symptoms during the last year. Use of illicit substances and substance abuse symptoms were associated with depressed mood.