5‐Hydroxytryptamine content of the whole blood in psychiatric illness and alcoholism

5-Hydroxytryptamine (5HT, serotonin) content of the whole blood has been measured in hospitalized groups of manic, depressed, schizophrenic and alcoholic patients; values were compared to non-psychotic controls. Only depressives had significantly different values. Alcoholics occupied an intermediate position between depressives and controls. Schizophrenics had virtually the same average level. Manic patients showed a very weak tendency toward higher values. Neuroleptic drugs in mania did not alter the blood 5HT levels, but in depression tricyclic antidepressants caused an elevation after 3 weeks of treatment. These post-treatment levels no longer differed significantly from those of non-psychotic controls.