Three mechanisms of lithium transport across erythrocyte membrane [lithium-sodium countertransport (LSC), lithium-potassium cotransport (LPC), and passive lithium diffusion (PLD)] were estimated in 27 acutely schizophrenic patients, 27 acutely depressed affective patients and in 18 control subjects. The activities of all mechanisms studied were significantly lower in both schizophrenic and depressed patients compared with controls. Analysis by gender showed that in control subjects, mean values of erythrocyte LSC and LPC were significantly higher in males compared with females. The decrease of LSC and LPC in depression and LSC in schizophrenia compared with control subjects was observed only in male patients but not in female ones. The results obtained suggest that lithium transport abnormalities during acute psychotic episodes are not specific to affective patients where lithium exerts its therapeutic action, but are also observed in schizophrenia. These abnormalities are more evident in male patients.