 Twelve subjects with current diagnosis of depressive episode will be recruited to undergo a brief course of 4 intravenous infusions of ketamine, given twice weekly for two weeks in combination with CBT, given twice weekly. The CBT course will be 16 total sessions given over 8 weeks, will begin the day following the initial ketamine infusion, and will be performed by a therapist who has successfully completed extensive training at the Beck Institute for Cognitive Therapy and Research and has experience with similar studies. Homework assignments will include thought records and activity charts which are used in standard practice to facilitate CBT interventions. 