It seems unlikely that a solitary disturbance in serotonin function can fully account for the pathophysiology of obsessive compulsive disorder. The authors propose that some forms of obsessive compulsive disorder, e.g., obsessive compulsive disorder with a history of Tourette's syndrome, may involve a relative or absolute derangement in both brain serotoninergic and dopaminergic systems. A role for dopamine in the pathophysiology of obsessive compulsive disorder is supported by a review of the preclinical and clinical evidence. Additional studies are needed to more directly evaluate dopamine function in patients with obsessive compulsive disorder.