Spectrofluorometric assays of DA, 5-HT and 5-HIAA were performed in different areas of postmortem brains of humans who died in hepatic and uremic coma. Brain DA showed a mild general decrease, the average reduction being 20 to 30 percent of the controls. By contrast, 5-HT and 5-HIAA were markedly increased in most brain areas, most significantly in the reticular and raphé nuclei of the brainstem and in some parts of the limbic system. Despite individual and regional differences, the monoamine changes had similar patterns in both hepatic and uremic coma. These data in human brain which confirm previous clinical and experimental studies in hepatic encephalopathy suggest some common disorders of central monoamine metabolism in endotoxic coma of different origin. Brain edema, a constant feature in toxic coma, is probably due to increased 5-HT content in the brain, the pathophysiologic effect of 5-HT on the blood-brain barrier being well established. The prominent changes of indoleamine metabolism in the reticular brainstem and limbic systems may be related to disorders of consciousness.