GSK598809 is being developed as an innovative treatment for substance dependence and potentially other compulsive behavioral disorders. This study will asses the effects of a single dose of GSK598809 in modulating nicotine reward in 2 cohorts of otherwise healthy male volunteers who smoke. Each cohort of subjects will receive a single dose of placebo or GSK598809 in two dosing sessions binded crossover fashine. There will be a washout period of at least seven days between each session.

Inclusion Criteria:

• Healthy male smokers aged 18-65 with a desire to quit smoking.
• Body weight greater than 50kg and BMI within range 19 - 29.9 kg/m2
• Healthy with no significant medical, psychiatric or laboratory evaluation abnormality.

Exclusion Criteria:

• Positive pre-study urine drug/breath alcohol screen: positive HIV 1/2, Hepatitis B or Hepatitis C test at screening.
• History of alcohol/drug abuse or dependence (other than nicotine) within 12 months of the study.
• History of psychiatric disorder or sensitivity to any of the study medications or components thereof or a history of drug or allergy that in the opinion of the physician responsible contraindicates their participation.
• History of cardiac or pulmonary disease/abnormalities.

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.