The investigators are conducting an open, uncontrolled study of ketamine in treatment-refractory OCD. Ketamine is a potent antagonist of the N-methyl-D-aspartate (NMDA) receptor and has been demonstrated to have rapid anti-depressant effects in patients with Major Depressive Disorder. The investigators have additionally provided evidence for rapid improvement of comorbid OCD and trichotillomania after ketamine infusion in a depressed woman.