Patients who have been diagnosed with OSA following routine clinical sleep studies will be asked to participate. Participation involves agreeing to two additional full night studies in the sleep laboratory, separated by 1 week. Both studies will be identical to the routine clinical studies, except that the patient will be asked to swallow a capsule containing either placebo or 250 mg cycloserine 1 to 2 hours prior to going to sleep. The order of the Placebo and Test nights will be randomized. The patient will be monitored continuously by a dedicated, senior polysomnography technologist.