Preventing drug use is a priority health objective for the United States. Although families have profound influence on their children, few rigorous evaluations of the influence of family-based interventions designed to prevent drug use in general adolescent populations have been reported. The purpose of the proposed research is to evaluate the influence on adolescent drug use of a family-directed drug prevention program. Tobacco and alcohol are the focal drugs. The program, delivered through the mail and follow-up telephone communications between health educators and parents, is based on propositions from adolescent drug research, is designed to maximize participation by families, and is practical in the sense that if found to be effective it can be administered through a variety of intervention modalities and readily distributed over large geographical areas at relatively low cost An experimental design will be used to assess the influence of the program on adolescent drug use. 880 adolescents ages 12 - 14 and their families will be entered into the study. Data will be collected from adolescents in their schools at baseline and at follow-up using self-administered questionnaires. Data will be collected by telephone from parents. Multivariate analyses will assess the influence of the intervention on adolescent drug use, identify the variables through which effects occurred, determine whether intervention effects varied according to selected characteristics, and assess the propositions that are basis for the intervention.