This paper examined changes in the influence of parents' and close friends' smoking on smoking transitions occurring over the course of adolescence, using a large (N=6,006) longitudinal study. The three grade periods were 5th to 7th (ages 10-12), 7th to 9th (ages 12-14), and 9th to 12th grade (ages 14-17). Smoking transitions examined were: (1) never to trying, (2) trying to monthly, and (3) monthly to daily. Results showed that the influence of parents' smoking was substantial for all three transitions during most of the grade periods and, for the transition from monthly to daily smoking, increased (p=.006) during adolescence. In contrast, the influence of close friends' smoking was strongest for the transition to trying smoking and did not significantly change (all p>.05) for any of the smoking transitions as the adolescent became older. In conclusion, the influence of close friends' smoking on smoking transitions might be stable during adolescence whereas the influence of parents' smoking on the transition to daily smoking might markedly increase across adolescence.