Objective: The fact that some antidepressants with strong effects on serotonin reuptake blockade fail to relieve obsessive-compulsive symptoms has caused growing interest in investigating noradrenergic function in obsessive-compulsive disorder (OCD) . In light of the above, we undertook a trial to investigate whether the combination of citalopram with nortriptyline is more effective in treating obsessive-compulsive symptoms than citalopram alone. Method: 40 patients who met the DSM-IV criteria for OCD were included in the study. Patients were allocated in a random fashion: 20 patients to citalopram 40mg /day plus nortriptyline 50mg /day, and 20 patients to citalopram 40mg /day plus placebo. Results: Both protocols significantly decreased the scores of the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) over the trial period, but the combination of citalopram and nortriptyline showed a significant superiority over citalopram alone in the treatment of OCD. Conclusion: As this study indicates, nortriptyline improves the efficacy of citalopram. In addition, a rapid onset of action is one of the advantages of this combination. This study supports further investigation of the noradrenergic– serotonergic hypothesis in OCD