1. Obsessive compulsive disorder and affective disorder have been investigated by means of various biological challenges. 2. Total sleep deprivation and methylphenidate challenge were used to determine the effects on a group of subjects with obsessive compulsive disorder. 3. The findings of a lack of response to total sleep deprivation and methylphenidate in obsessive compulsive patients contrasts with the findings in affective disorder patients. 4. The findings are more consistent with those in studies of panic disorder. 5. The relationship of obsessive compulsive disorder to affective and anxiety disorder may be elucidated by further studies.