Five hundred and seven students 14- to 16-years-old gave self-report responses to a substance use questionnaire, the Norwicki-Strickland Locus of Control Scale, and The Piers-Harris Children's Self-Concept Scale. Path analysis revealed that the influence of peers' and parents' use and norms on adolescents' alcohol and tobacco use is mediated by personality, age, sex, and social status effects. Adolescents with external locus of control or low self-esteem "behavior" were more influenced by their peers to smoke. Younger students and girls were more influenced by parental norms than were older students and boys, but only for alcohol and not for tobacco use. Other findings were that girls were not as strongly influenced by their own norms and that girls and low social status adolescents were more influenced by their friend's smoking and drinking. The peers' findings are discussed in relation to substance prevention strategies.