The current prevalence of drug use among American high school seniors, and trends in drug use since 1975, were investigated as part of the program entitled “Monitoring the Future: A Continuing Study of the Lifestyles and Values of Youth,” funded by the National Institute on Drug Abuse. The basic research design involved data collection from high school seniors in approximately 125 public and private high schools across the United States, beginning with the class of 1975. Subjects were asked to respond to questionnaire items about current drug use, use at earlier grade levels, degree and duration of “highs,” attitudes and beliefs, and their social milieu. Results indicated that: (1) 65% had used illegal drugs at some point in their lives with a substantial proportion having used only marihuana; (2) cigarettes were used daily by more of the students than any other drug; (3) more students used marihuana daily as compared to alcohol; and (4) higher proportions of males than females were involved in drug use, especially heavy drug use. (Author/HLM)