Reports the case of a 35-yr-old depressed male who had total gastrectomy 9 yrs previous to a suicide attempt. While chlorpromazine & electroconvulsive therapy were not effective, 1,000 mcg of vitamin B12 produced complete remission within 8 days. Results suggest that B12 therapy may be indicated in all psychiatric patients with a concurrent physical illness which predisposes to B12 deficiency.