This randomized, placebo-controlled phase 1/2 trial evaluated the safety and immunogenicity of four doses of a nicotine vaccine in smokers and nonsmokers. Subjects were 21 smokers and 9 nonsmokers in good physical and mental health. They were aged 24-60 years, were recruited from the general public using newspaper advertisements, and were evaluated at University Hospital Maastricht. Each volunteer received four spaced intramuscular injections of 100 microg of purified 3'-aminomethylnicotine conjugated to detoxified Pseudomonas aeruginosa r-exoprotein A or placebo both adsorbed to 800 microg aluminum into the deltoid muscle of alternating arms. Clinical safety was determined by vital signs, reactogenicity, and adverse events, and immunogenicity was measured by enzyme-linked immunosorbent assay. Intensive follow-up for 266 days revealed the vaccine to be well tolerated. We found no significant differences in adverse events between the vaccine and placebo groups. Significant increases in the geometric mean titer (GMT) levels of nicotine-specific antibodies were observed from 7 days after the second vaccination (day 21), reaching nicotine-specific antibody levels of at least 8 microg/ml in half of the subjects (50%) at day 49. A fourth dose administered at day 182 significantly boosted waning antibody levels to a GMT of 10.8 microg/ml at day 217 (95% CI 6.0-19.3). Results showed that the immunogenicity of the vaccine was not impeded by the presence of nicotine. These observations provide evidence in humans that the vaccine we used may represent a feasible strategy for evoking type-specific antibodies against nicotine.