BACKGROUND Uncontrolled reports suggest that intravenous clomipramine hydrochloride may be effective for patients with obsessive-compulsive disorder (OCD) who are nonresponsive to oral clomipramine. METHODS Fifty-four patients with oral clomipramine-refractory OCD were randomized to receive 14 infusions of either placebo or clomipramine hydrochloride, starting at 25 mg/d and increasing to 250 mg/d. Ratings were conducted double-blind after infusion 14 among 54 patients, single-blind 1 week later among 39 patients, and nonblind 1 month later among 31 patients. Response was based on a Clinical Global Impressions rating of at least "much improved." RESULTS Six (21%) of 29 patients randomized to receive intravenous (i.v.) clomipramine vs 0 of 25 patients given i.v. placebo were responders after 14 infusions (df = 1, P<.02). Dimensional ratings after infusion 14 revealed significant (P = .007) improvement on the National Institute of Mental Health-Obsessive-Compulsive Scale and the Clinical Global Impressions Scale (P = .03), but not the Yale-Brown Obsessive Compulsive Scale. One week later, all dimensional measures of OCD showed significant improvement. At 1 week post-i.v., 9 (43%) of 21 patients initially randomized to i.v. clomipramine and treated subsequently with oral clomipramine were responders, whereas 0 of 18 patients initially randomized to receive i.v. placebo and treated subsequently with several days of open-label i.v. clomipramine responded (df = 1, P<.002). Of the 31 patients assessed 1 month after i.v. infusion (treatment not controlled), 18 (58.1%) were responders. Intravenous clomipramine treatment was safe with no serious adverse consequences. CONCLUSIONS Intravenous clomipramine is more effective than i.v. placebo for patients with OCD with a history of inadequate response or intolerance to oral clomipramine. Further study of this promising treatment for refractory OCD is needed.