Vaccination against nicotine has been proposed as a potential treatment for nicotine dependence. Because vaccination may take months to elicit satisfactory antibody levels, the clinical usefulness of this approach will be enhanced if vaccination can be accomplished during continued nicotine intake (e.g., before a smoker quits). The current study examined the immunogenicity of a nicotine conjugate vaccine during continued nicotine dosing in rats, and its effects on nicotine distribution to brain. In the first experiment, nicotine was administered over 11 weeks as 20 intra venous (i.v.) bolus injections per day during the rat's active cycle to simulate the usual pattern of nicotine intake from cigarette smoking. In the second experiment, rats received a continuous s.c. infusion of nicotine by osmotic pump for 11 weeks to provide serum nicotine concentrations equivalent to those of a heavy smoker and 24 h/day nicotine exposure. Nicotine-specific antibody titers after the third booster dose were not compromised by either regimen of concurrent nicotine administration compared to those of rats receiving saline. A single additional i.v. nicotine dose was administered at the end of each experiment. The distribution of this single nicotine dose to brain was reduced by 40-60% in vaccinated rats compared to controls. Vaccine efficacy in reducing nicotine distribution to brain was not compromised by concurrent nicotine administration. These data suggest that vaccination during concurrent nicotine administration is feasible, and that the ability of vaccination to reduce nicotine distribution to brain is preserved even after months of nicotine dosing at rates approximating cigarette smoking.