Drawing on differential association and social learning theories, the research specified social processes such as socialization, group pressure, social selection, and rationalization which dictated causal pathways leading to and from drug use and then estimated reciprocal influences among differential association, social pressure from peers, attitudes favorable toward drug use, and individual drug use. Using data from the 1977-1979 National Youth Survey, a covariance structural equation model was estimated which allowed for correlated measurement error. Cross-sectional analyses revealed no main effects of overt peer pressure on drug use. Estimation of the reciprocal effects model also revealed overt peer pressure did not significantly influence drug use and did not mediate the effect of differential association. Instead, influences of socialization, social selection, and rationalization played important roles in understanding adolescent drug use. Supplemental data on the correlational analysis are appended. 82 references, 8 tables, and 5 figures