Results of treating depressive states (manic-depressive psychosis, involutional and vascular depressions) with S-methylmethionine (vitamin "U") are presented. The vitamin was found to produce a marked antidepressant effect in depressive states of various nosology irrespectively of the duration of the depression phase or preceding treatment. The authors suggest that studies of the effect of the vitamin and its clinical use as an antidepressant should be continued.