Abstract: Many drug-dependent adults began using drugs during adolescence. In fact, adolescent drug users are more likely to become drug-dependent adults than those abstaining from drug use until after the age of 18. Because of this, recent research has begun to investigate the consequences of adolescent drug use. Specifically, research has begun to focus on the behavioral effects of drugs on the developing brain and the development of drug addiction. The present study examined the responsiveness of the mesolimbic dopamine (DA) pathway during development through the use of in vivo microdialysis. Specificall, it was determined whether nicotine-induced accumbal DA release differs between adolescent and adult rats. To assess nicotine's effects across age, animals received acute or repeated nicotine at early adolescence (postnatal day (PND) 35), late adolescence (PND 45), or young adulthood (PND 60). Findings suggest that there are significant differences between adolescent and adult animals in their dopaminergic response to nicotine. Adult animals had an enhanced DA response to acute nicotine challenge, an effect absent in adolescence. Additionally, this nicotine-induced increase in adults was not apparent after repeated nicotine treatment. These results provide insight into how the adolescent brain responds to nicotine and may also provide evidence as to how prolonged nicotine use affects normal brain development and responsiveness.