The alpha 2-adrenergic receptor antagonist yohimbine was administered to 12 drug-free patients with obsessive compulsive disorder (OCD) and to 12 healthy subjects. Changes in behavior, cardiovascular symptoms, and in plasma levels of cortisol and the norepinephrine metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), were assessed. Yohimbine had no significant effect on OCD symptoms. The OCD patients did not differ from healthy controls in their behavioral and MHPG response to yohimbine. In contrast to healthy subjects, OCD patients, like previous reports of depressed and panic disorders patients, had an increased cortisol response to yohimbine. These data suggest it is unlikely that abnormal noradrenergic function plays a primary role in the pathogenesis of OCD.