The surveys were conducted in 1983, 1990, and 1994 and used representative samples from randomly selected public school districts and private schools throughout the State, with nearly identical multistage sampling procedures. Analysis of variance was used to test the significance of the trends and to identify meaningful differences in trends by demographic subgroups, based on gender, grade level in school, and ethnicity. Adolescent alcohol and drug use declined in the 1980's and then increased from 1990 to 1994. Trends in friends' drug use and school problem behavior paralleled the trends in use of alcohol and other drugs; these findings were consistent with these behaviors' being part of the same adolescent problem behavior syndrome. Parental disapproval also followed a trend consistent with the drug use trends; parental disapproval increased in the 1980s and then decreased in the 1990s. However, the trend in school prevention influences did not parallel these drug use trends; student exposure to school-based primary prevention programs continued to increase from 1990 to 1994. The use of alcohol, cigarettes, marijuana, and other illicit drugs increased fastest among the younger students during 1990-94, despite increased exposure to school-based prevention programs. Findings indicated the need for prevention efforts targeted at younger adolescents in middle school and early high school, for prevention efforts aimed at a broad range of deviant behaviors rather than only at drug use, and for continuing research on juvenile drug abuse causes. Tables, notes, and 25 references (Author abstract modified)