The possibility that convulsive therapy might produce damage in the central nervous system led us to investigate the effect of metrazol convulsions on the brains of monkeys. The neuropathologic data obtained from these experiments are reported in this paper. At the same time we shall report clinical observations on 41 patients who underwent metrazol therapy. Special attention is directed to 3 cases of this group in which serious cardiac complications occurred and to 1 case in which a flare-up of latent bone disease was noted after treatment. EXPERIMENTAL METHOD Seven monkeys (Macacus rhesus), weighing between 2 and 6 Kg., were given intra-arterial injections of metrazol, in amounts varying from 5 to 30 mg. A standard 10 per cent solution of metrazol, buffered with dibasic sodium phosphate (Na2HPO4), was used. The experiment was planned to follow as closely as possible the clinical application of metrazol therapy. Because of