A significant increase in S-urate was found postictally in 17 patients with two or more grand mal seizures within 24 h. In six patients S-urate was above the level at which hyperuricemic renal failure may develop. Impaired renal function was observed in two patients who had extremely high S-urates. It is proposed that prophylactic procedures against hyperuricemic renal failure should be carried out in all patients with repetitive convulsions.