A two-part report presents the results of the 16th national survey of American high school seniors, and the 11th national survey of American college students. This volume contains the results from high school seniors. Chapter 1 explains the purposes and rationale for the research, and content areas covered in the report. Chapter 2 presents an overview of the key findings. In chapter 3 the research design, sampling plans, and field procedures used in both the in-school surveys of seniors, and the follow-up surveys of young adults are presented. Chapter 4 summarizes the levels of drug use reported by the high school class of 1990, and chapter 5 summarizes trends in drug use, comparing the 16 graduating classes of 1975 through 1990. Chapter 6 discusses the issue of drug use at earlier grade levels. Chapter 7 presents results from questions examining the degree and duration of highs among seniors. Chapter 8 presents the cross-time results for three sets of attitude and belief questions. Data pertaining to the social milieu of young people are presented in Chapter 9, including parental and peer attitudes and exposure to drug use by friends and others. Additional recent findings from the Monitoring the Future study are presented in chapter 10. The findings focus on the use of nonprescription stimulants; the use of marijuana on a daily basis; racial/ethnic differences in drug use; explaining declines in marijuana and cocaine use; and changes in drug use during pregnancy. Extensive tables and figures are included. (LLL)