This study focus on modeling environmental covariates of monthly changes in substance use (i.e., tobacco, marijuana, alcohol). Using structured protocol, monthly interviewers were conducted of 181 young adolescents, ages 11-14, and their parents. Composite scores were derived from their monthly telephone reports describing variation in parent involvement, exposure to peer deviance, peer conflicts, and level of family stress. Interviews were analyzed as separate observations, using generalized estimation equations. Consistent with an ecological framework on development, environmental covariates varied by gender-and family- constituency. Across gender in both 1- and 2-parent families, exposure to peer problem behavior covaried with increased substance use in the same month. Other monthly predictors varied by gender. Findings suggest interventions programs for high-risk youth targeting adolescent problem behavior need to focus on substance use and managing the peer environment.