Fourth-year medical students at 13 medical schools in different regions of the United States received an anonymous questionnaire designed to examine their current and prior use of 11 substances and their attitudes toward substance use among physicians. Of 1,427 questionnaires distributed, 41 percent were returned. The questionnaire and distribution method were derived from an ongoing survey on drug use in order to permit comparison of the medical students with a national sample of age- and sex-matched cohorts. The rates of substance use during the 30 days preceding receipt of the questionnaire were: alcohol, 87.8 percent; marijuana, 17.3 percent; cigarettes, 9.0 percent; cocaine, 5.6 percent; heroin, 0.0 percent; other opiates, 0.9 percent; LSD, 0.2 percent; other psychedelics, 0.5 percent; barbiturates, 0.5 percent; tranquilizers, 2.2 percent; and amphetamines, 1.2 percent. Compared with their age and sex cohorts nationally, the medical students reported less use of marijuana, cocaine, cigarettes, LSD, barbiturates, and amphetamines. However, their use of other opiates was approximately the same and their use of tranquilizers and alcohol was slightly higher than that of the other cohorts. Data on their sources of knowledge about drug abuse indicate the need for greater attention to this issue in the medical curriculum.