Two of the major topics treated in this report are the current prevalence of drug use among American high school seniors, and trends in use since 1975. Also reported are data on school grade of first use, trends in use at earlier 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. The eleven separate classes of drugs distinguished are marijuana (including hashish), inhalants, hallucinogens, cocaine, heroin, natural and synthetic opiates other than heroin, stimulants, sedatives, tranquilizers, alcohol, and cigarettes. Separate statistics are also presented here for several sub-classes of drugs: PCP and LSD, barbiturates and methaqualone, and amyl and butyl nitrites. Occasions of medically supervised use of the psychotherapeutic drugs were excluded. Attention was focused on high frequency levels of drug use and an indirect measure of dosage per occasion was introduced to differentiate levels of drug use. The "Other Findings" section includes data on the use of non-prescription stimulants, daily marijuana use, effects of post high school environments and role transitions on drug use, and the issue of distinguishing maturational change from period effects and class cohort differences. Findings are supported by numerous tables. (Author/MCK)