This report is the twelfth in an annual series reporting the drug use and related attitudes of America's high school seniors, college students, and young adults. The findings, which cover the high school classes of 1975 through 1988, come from an ongoing national research and reporting program entitled "Monitoring the Future: A Continuing Study of the Lifestyles and Values of Youth." Two of the major topics which continue to be included in this series are the current prevalence of drug use among American high school seniors and trends in use by seniors since the study began in 1975. Distinctions among important demographic subgroups in the population are made, and this year for the first time distinctions among various socioeconomic levels are included. Also reported are data on grade of first use, trends in use at lower grade levels, intensity of drug use, attitudes and beliefs among seniors concerning various types of drug use, and their perceptions of certain relevant aspects of the social environment. Data on the prevalence and trends in drug use among young adults (late teens to the late twenties) who have completed high school are also incorporated into this report series. The continuing epidemic of cocaine use among young adults makes this an age group of particular importance. Two chapters in this report present data on college students specifically. Trends are presented on drug use among college students since 1980--the first year in which a good national sample of college students 1 to 4 years past high school was available from the follow-up survey. (ABL)