Results are based on findings of surveys of a representative sample of high school seniors conducted from 1975 through 1987. In addition, surveys include subsamples of participants from each previously graduating class. While the use of most drug classes showed declines or remained steady in 1987; marijuana, cocaine, and stimulants continue to be used by appreciable proportions of youth and young adults. Alcohol use in 1987 is almost universal, with 92 percent of seniors having tried it, and active use is widespread. Occasions of heavy drinking (five or more drinks in the prior 2 weeks) was reported by 38 percent of seniors and 43 percent of college students. Males were more likely than females to report both drug and alcohol use. Cigarettes continued to be the class of substance most often used on a daily basis by high school seniors in 1987, with smoking being more frequent among the non-college bound and among females. While daily smoking rates declined considerably from 1977 to 1981 (from 29 to 20 percent), they declined by only 1.6 percent since then. While results indicate some improvement, by age 27, 80 percent of respondents had tried an illicit drug, 60 percent had tried a drug other than marijuana, and 40 percent had tried cocaine. Thus, it remains true that this Nation's youth and young adults show a level of involvement with illicit drugs that is greater than is found in any other industrialized Nation. 50 tables, 67 figures and 2 appendixes.