A total of 20 subjects will participate in this four week, between groups, double-blind, placebo controlled study. Subjects will participate in two experimental sessions separated by approximately one week. Subjects will be randomized to receive either 50 mg cycloserine or placebo combined with cue exposure. Several physiological and subjective outcome measures (e.g., heart rate, blood pressure, galvanic skin response) will be obtained during the sessions. Experimental sessions will last approximately 4.5 hours with follow-up sessions lasting approximately thirty minutes. Our aims are:

1. To examine the effect of cycloserine vs. placebo on extinction of smoking cue reactivity in overnight abstinent smokers. Reactivity to smoking cues will be captured with self-report smoking urges and physiological measures (heart rate, blood pressure, and skin conductance).

   We hypothesize that cycloserine, relative to placebo, will facilitate extinction of smoking cue reactivity.

2. To examine the effect of cycloserine vs. placebo when combined with two 4.5 hour laboratory cue exposure training sessions, on smoking behavior in smokers. Smoking behavior will be measured with self-report smoking and saliva cotinine levels.
3. To examine the effect of cycloserine vs. placebo on memory performance in nicotine dependent smokers. Memory performance will be measured with verbal learning, recognition and recall tasks.

4) To examine the safety and tolerability of cycloserine treatment in smokers. We hypothesize that cycloserine will be well tolerated by smokers.