 Ketamine has been shown to have an antidepressant effect when given intravenously in doses of 2mgkg. Ketamine is used as a standard induction drug during general anesthesia. It is known in this instance to decrease postoperative pain. No one has studied whether or not ketamine when given in doses used during general anesthesia 0.5mgkg intravenous has an antidepressant effect on surgical patients who suffer from depression. The study is designed to determine whether or not a small dose of ketamine when given at the induction of anesthesia could have an antidepressant effect on surgical patients with depression. 