During the first year of the study, data were collected from 1,634 7th, 8th and 9th grade students at 11 schools in Los Angeles County, Calif. Of the original sample, 847 students were selected to participate in the 5-year study from 1975 to 1980. The sample was 33 percent male, 67 percent female, 13 percent Hispanic, 15 percent black, 8 percent Asian, and 64 percent white. Five different substances were studied: cigarettes, alcohol, cannabis, nonprescription medications, and hard drugs. Results showed that there were significant and consistent relationships between current level of substance use and intention of use of all ethnic groups. However, these measures of association varied considerably among ethnic groups and covered a wide range from .17 for blacks on use of nonprescription medications to .69 for Hispanics on alcohol consumption. Results indicate the degree of association between intention and use, as well as ethnic differences, gradually decreased over time. Also, partialling out the effects of previous experimentation with drugs decreased the contribution of intention to predict future drug use to a nonsignificant level for Hispanics, to a moderate degree for blacks and Asians, and remained a significant and meaningful contribution for whites. Tabular data and 8 references. (Author abstract modified)