The survey was administered by direct mail to a random sample of 2,200 students at a large southwestern U.S. university. The survey instrument consisted of 174 items that purported to measure personal substance use behavior, perceived substance use of other students, frequency of behavior associated with substance use, motivations for substance use, consequences of substance use, attitudes toward substance use relative to school and health, demographics, and miscellaneous items. The study focused on the use of alcohol, marijuana, cocaine, amphetamines, barbiturates, tranquilizers, psychedelics, and designer drugs. All analyses that involved the motivation items included only those respondents who reported being current drug users, two subscales were developed, one for each category of motivations. Reliability for each subscale as estimated by coefficient alpha was .80 and .86, respectively. A series of stepwise multiple regression analyses were computed in which individual drug-use indexes served as criterion variables; the predictor variables were the personal motivations subscale (PMS) and the social motivation subscale (SMS) for each model. Results indicate that the PMS was the stronger predictor in every model, with the exception of the model that predicted the alcohol-use index. The SMS was the best predictor for alcohol use. 5 tables and 17 references