The evidence linking biogenic amines and affective disorders is critically reviewed. Surveyed are studies on the level of biogenic amines and their metabolites in the brain, blood, urine and cerebrospinal fluid of patients with affective conditions; the effects of biogenic amine precursors, depletors and blockers on affective states and the action of present methods of treatment of these disorders on the level of biogenic amines. Reference is also made to the existence of various disease states where abnormalities of biogenic amines exist in the absence of affective disorders. The review fails to uncover convincing evidence that affective disorders are related to abnormal levels of biogenic amines. Reasons are outlined why the "catecholamine hypothesis" and related theories can neither be proven nor disproven with the available techniques.