Abstract: Despite the high prevalence of adolescent smoking, few studies have examined nicotine sensitivity during this developmental period. In the present study we examined adolescent and adult rats' preference/aversion for a flavor previously paired with nicotine. Paired (nicotine + Kool-Aid) and unpaired (Kool-Aid) solutions were presented in the home cage on alternating nights, with water given during the light phase for six days. A choice test was conducted 24 hr after the last night of conditioning, with both flavors presented simultaneously during the dark cycle. On test day, although the flavor previously paired with nicotine was not preferred at either age, adolescent rats consumed significantly more of the paired flavor than adults. These results suggest that adolescent rats are less sensitive to the aversive properties of nicotine. This finding taken together with adolescents' increased sensitivity to the rewarding properties of nicotine, may result in an increased vulnerability to nicotine dependence.