Blood and serum concentrations of selenium have been determined in a group of psychiatric patients and in 35 healthy controls. The psychiatric group consisted of 14 schizophrenics, seven paranoid disorders, six affective psychosis (manic-depressive), four reactive psychosis, 11 dementia senilis, 17 with a diagnosis of neurosis and two with delirium tremens. Normal values were found in all groups except for delirium tremens where decreased blood and serum values were found.