Acute administration of nicotine increases cortisol and prolactin but the endocrine effects of tobacco withdrawal are unknown. In a residential, double-blind, placebo-controlled, crossover study, volunteers smoked ad lib for 4 days and underwent monitored tobacco abstinence for 3 days. On no-smoking days, patches delivering 0, 10, 20, or 30 mg nicotine were applied for 16 h. Daily plasma samples were analyzed for ACTH, cortisol, and prolactin. During nicotine abstinence (0 mg patch), circulating levels of ACTH, cortisol, and prolactin did not significantly change from ad lib smoking levels. Over all the patch conditions there was a significant effect of day, with modest but significant elevations of cortisol and ACTH levels on the second no-smoking day (Wed, 37 h abstinent). Prolactin levels increased during nicotine abstinence, but this effect was not significant. The observed endocrine changes did not correlate with physiologic, performance, or subjective measures of tobacco withdrawal. Our data indicate endocrine changes during acute tobacco withdrawal are transient and small. Thus, the present results do not support the use of ACTH as a treatment for tobacco cessation.