The val allele of the catechol-O-methyltransferase (COMT) val(158)met polymorphism has been linked with nicotine dependence and with cognitive performance in healthy volunteers. We tested the hypothesis that the val allele is a risk factor for altered brain function and cognition during nicotine abstinence as compared with the normal smoking state. Chronic smokers (n=33) were genotyped prospectively for the COMT polymorphism for balanced selection of met/met, val/met and val/val groups. A visual N-back working memory task was performed during two separate blood oxygen level-dependent (BOLD) functional magnetic resonance imaging sessions in counterbalanced order: (1) smoking as usual, and (2)>or=14 h confirmed abstinence. Significant genotype by session interactions were observed for BOLD signal in right dorsolateral prefrontal cortex (DLPFC; (P=0.0005), left DLPFC (P=0.02) and dorsal cingulate/medial prefrontal cortex (P=0.01) as well as for task reaction time (P=0.03). Smokers with val/val genotypes were more sensitive to the abstinence challenge than carriers of the met allele, with the greatest effects on BOLD signal and performance speed at the highest working memory load. These data suggest a novel brain-behavior mechanism that may underlie the increased susceptibility to nicotine dependence and smoking relapse associated with the COMT val allele. Exploration of the effects of COMT inhibitors as a possible smoking cessation aid in this group may be warranted.