1. The role of serotonin in the aetiology of obsessive compulsive disorder (OCD) has been established through considerable indirect evidence (Landry and Chouinard, 1990). The strongest evidence comes from the fact that drugs known to be serotonin-selective reuptake inhibitors (SSRIs) have been found to be useful in the pharmacotherapy of OCD (Landry and Chouinard, 1990). 2. The authors investigated a new treatment approach by adding an adrenal steroid suppressant to a SSRI, fluoxetine, in the case of a severe obsessive-compulsive patient who was drug-resistant to clomipramine and SSRIs. 3. We found that the combination of aminoglutethimide 250 mg qid and fluoxetine 40 mg die significantly improved the patient's condition. Moreover, during a four and a half year period, each time we tried to decrease either fluoxetine or the steroid suppressant, the patient started to relapse, suggesting that the adrenal steroid suppressant had a potentiating effect on the SSRI.