NicVAX, a nicotine vaccine (3'AmNic-rEPA), has been clinically evaluated to determine whether higher antibody (Ab) concentrations are associated with higher smoking abstinence rates and whether dosages and frequency of administration are associated with increased Ab response. This randomized, double-blinded, placebo-controlled multicenter clinical trial (N = 301 smokers) tested the results of 200- and 400-µg doses administered four or five times over a period of 6 months, as compared with placebo. 3'AmNic-rEPA recipients with the highest serum antinicotine Ab response (top 30% by area under the curve (AUC)) were significantly more likely than the placebo recipients (24.6% vs. 12.0%, P = 0.024, odds ratio (OR) = 2.69, 95% confidence interval (CI), 1.14-6.37) to attain 8 weeks of continuous abstinence from weeks 19 through 26. The five-injection, 400-µg dose regimen elicited the greatest Ab response and resulted in significantly higher abstinence rates than placebo. This study demonstrates, as proof of concept, that 3'AmNic-rEPA elicits Abs to nicotine and is associated with higher continuous abstinence rates (CAR). Its further development as a treatment for nicotine dependence is therefore justified.