THIS paper presents the results of a three-year study of catecholamine excretion patterns during acute psychotic and neurotic depression, and represents part of an ongoing research program on biochemical and behavorial aspects of depression. It has been suggested by a number of researchers that there may be biochemical factors of etiological importance in depression which are most likely to be evident in severe psychotic depressive reactions, rather than in the milder neurotic group. In this study, we wish to determine: (a) whether changes in levels of excretion patterns in norepinephrine and its breakdown products occur in depression; (b) if such changes occur, are they characteristic of a clinically defined subgroup of depressed patients; and (c) do these changes yield information suggesting an alteration in either of the two major enzymes involved in the breakdown of norepinephrine (Fig 1). Evidence indicates the importance of norepinephrine