Data were obtained from high school seniors during the spring of each year in a sample of approximately 125 to 140 public and private high schools selected to provide an accurate cross-section of high school seniors throughout the United States. Completed questionnaires were obtained from 77 to 83 percent of all sampled students in participating schools each year. Study findings revealed that American youth continued to gradually moderate their use of illicit drugs over the 1975-1982 period. Between 1981 and 1982, nearly all classes of illicit drugs showed declines in current use with the most appreciable drops occurring for marijuana, cocaine, stimulants, and sedatives. Tranquilizer and hallucinogen use also declined but more modestly, and opiates other than heroin exhibited some evidence of decline. Stimulants, the second most widely used class of illicit drugs, showed a different pattern of change than most other drugs. Stimulant use was fairly steady between 1975 and 1979 and then rose rapidly for 2 years, while most other drugs were starting to fall in popularity. Over-the-counter diet pills had been used by a sizable proportion of high school seniors, while stay-awake pills were used by fewer students. Alcohol use remained relatively stable over the period. A rather large drop in daily smoking rates was attributed to personal concerns about the health consequences of use and perceived peer disapproval. 19 tables and 37 figures