This report is the 10th in an annual series reporting the drug use and related attitudes of American high school seniors. Findings reported cover the high school classes of 1975 through 1986 and come from the national project, Monitoring the Future: A Continuing Study of the Lifestyles and Values of Youth. Findings on the prevalence of, and trends in, drug use and related factors are reported separately for high school seniors and for two subsamples of young adults who had participated in the study as high school seniors: young adults post-high school and college students. Trend data are presented for varying time intervals. For high school seniors, drug use by grade level, degree and duration of drug highs, attitudes and beliefs about drugs, and the social milieu are also examined. A section entitled "Other Findings From the Study" explores the use of nonprescription stimulants, daily use of marijuana, medically supervised use of psychotherapeutic drugs, correlates of cigarette smoking, and other data on correlates and trends. Eleven separate classes of drugs are discussed: (1) marijuana (including hashish); (2) inhalants; (3) hallucinogens; (4) cocaine (including crack); (5) heroin; (6) other natural and synthetic opiates; (7) stimulants; (8) sedatives; (9) tranquilizers; (10) alcohol; and (11) cigarettes. Separate statistics are presented for several subclasses of drugs. Estimates adjusted for absentees and dropouts are appended. Forty data tables and 65 figures are included. (NB)