Cognitive Remediation With D-Cycloserine

One hundred seventy-five eligible participants will be enrolled with aim of randomizing 60 to a double-blind, placebo-controlled trial of D-cycloserine added to cue-exposure treatment to prevent relapse to smoking. Subjects who sign an informed consent, meet inclusion criteria, and demonstrate response to cue reactivity at the screening visit, will either be: * started on approximately 3 weeks of either nicotine replacement therapy (NRT) at a dose of either 14 or 21 mg/day or varenicline titrated to 1.0 mg bid; decision of which method to use to quit smoking will be based on participant choice as well as taking into account any medical contraindications to either therapy. * evaluated to confirm abstinence from smoking. Recently abstinent participants referred by a smoking cessation clinic, PCP or self referred must have an expired air CO < 10 ppm to confirm abstinence. Subjects who are able to demonstrate 18-24 hours of abstinence prior to the first Cue Exposure Therapy Visit (CET I) will be eligible to be randomized to two visits of study medication and cue exposure treatment, spaced five to nine days apart. Subjects will complete 2 follow-up visits at 2-4 days and four weeks after the last CET visit. The entire study involves twelve visits and will last approximately ten weeks. For recently abstinent participants referred by a smoking cessation clinic, PCP or self referred, the study involves 7 visits (screening and baseline visit will be merged into one and there is no CBT component) and will last approximately 7 weeks.