Three male chronically psychotic patients (mean age 33.0 +/- S.D. 7.2 years), two with schizoaffective disorder and one with organic affective disorder, received carbamazepine (CBZ) because of affective symptoms (and, in one case, partial complex seizures) refractory to management with antipsychotic drugs. Coincident with CBZ administration (and clinical improvement), hyponatremia developed thought to be due to the antidiuretic effect of this drug. Lithium was added to counteract the antidiuretic effect of CBZ. Further clinical improvement ensured, serum sodium levels became normal, and there was an increase in the white blood cell count in each patient. The clinical implications of our findings are discussed.