Study to investigate the safety, tolerability and pharmacokinetics of GSK598809 in otherwise healthy volunteers. This study is required because this drug is being developed for the treatment of nicotine dependence. It is important to evaluate how this drug interacts in healthy smokers. The study is planned to consist of a single part, with 4 dosing periods. Subjects will receive 3 escalating doses of GSK598809 and 1 dose of placebo. There will be at least 1 week of wash out between doses. In each dosing period 14 subjects will receive escalating doses and 4 subjects will receive placebo. The actual doses used will be determined based on the safety/ tolerability and pharmacokinetics during the previous dose. It is expected that the duration of this study will be approximately 10 weeks.