Smoking-related behaviors and attitudes of significant others (especially friends and parents) are among the most consistent predictors of adolescent smoking. However, theorists remain divided on whether the behaviors of significant others influence adolescent smoking directly or indirectly, and the relative influence of parental and peer smoking on adolescents' own smoking is still a matter of debate. In addition, little research has examined the role of significant others' behavior on different stages of smoking onset. In particular, not much information is available regarding gender and ethnic differences in social influences on smoking behavior. We use structural equation modeling to address these issues. Different theoretical perspectives from cognitive-affective theories (Ajzen 1985; Ajzen and Fishbein 1980) and social learning theories (Akers et al. 1979; Bandura 1969, 1982, 1986) have been integrated into a structural model of smoking influence. The results show that friends' smoking affects adolescent initiation into smoking both directly and indirectly, whereas parental smoking influences smoking initiation only indirectly. The data also show that friends' and parents' smoking affect smoking escalation only indirectly. In general, friends' smoking has a stronger effect on adolescents' smoking behavior, particularly on initiation. Multiple group comparisons of the structural models predicting smoking initiation among males and females reveal that parental approval of smoking plays a significant mediating role for females, but not for males. Comparisons of Whites, Blacks, Hispanics, and other ethnic groups reveal that there are some significant differences in the pathways of friends' influences among the four groups.