In continuing studies of drugs with antidepressant and antimanic effects, two monoamine oxidase (MAO) inhibiting agents with relatively specific actions in vitro on the two forms of MAO (MAO-A and MAO-B) have both been found to be clinically active antidepressants. Whether both drugs affect individual depressed patients equally and whether the in vitro specificity is maintained in vivo is under study using clinical and psychological assessment procedures, biochemical and neuroendocrine measures in blood and cerebrospinal fluid, as well as electrophysiological procedures. The blockade by lithium carbonate pretreatment of the stimulant effects of d-amphetamine has been found to be accompanied by changes in cortical average evoked responses and in the excretion of the catecholamine metabolite, 3-methoxy, 4-hydroxy phenyl glycol (MHPG). Fenfluramine's antidepressant effects were found to be accompanied by marked reductions in plasma norepinephrine levels. In other studies, psychological test differences between bipolar and unipolar depressed patients reported several years ago were found to be a replicable distinction in a new, larger patient sample. Other depression-related phenomena in verbal learning and information processing and in behavioral features have been objectively characterized. BIBLIOGRAPHIC REFERENCES: Buchsbaum, M.S., van Kammen, D.P. and Murphy, D.L.: Individual differences in average evoked responses to d-and l-amphetamine with and without lithium carbonate in depressed patients. Psychopharmacology 51: 129-135, 1977. Weingartner, H., Miller, H. and Murphy, D.L.: Mood-state-dependent retrieval of verbal associations. J. Abnormal Psychol. 86: 276-284, 1977.