In Study 1, ten never-smokers, ten ex-smokers and nine current smokers received nicotine (2 mg) and placebo gum hourly for 4 hours on 2 consecutive days in a randomized, double-blind, cross-over protocol. Dysphoria from nicotine was greatest in never-smokers, intermediate in ex-smokers, and least in current smokers (p less than 0.05). On the third day, subjects were given concurrent access to the same gums and told to chew ad lib. Across all subjects, nicotine was an aversive stimulus (i.e., self-administered less than placebo). Nicotine was avoided most in never-smokers, intermediate in ex-smokers and least in current smokers (p less than 0.05). Study 2 used a similar protocol and compared the nine current smokers in Study 1 who were not told they would receive nicotine with eight informed smokers, i.e., smokers told they would receive nicotine. Although nicotine appeared to be a reinforcer more often in the informed smokers than in the uniformed smokers (63% vs. 22%), this result was not statistically significant. Our results suggest 1) past drug history can influence the stimulus effects of nicotine and 2) the effects of instructions on the response to nicotine may be less in experimental settings than in therapeutic settings.