A controlled study of 5 patients with infantile spasms was performed to determine the effectiveness of corticotropin (ACTH) treatment. Patients were monitored serially, using a time-synchronized polygraphic and video system. Serum cortisol levels were determined by radioimmunoassay. Four patients showed total cessation of seizures and normalization of the EEG on low-dose ACTH therapy. Two of these patients became hypertensive, requiring discontinuance of ACTH. Serum cortisol levels increased markedly in all patients after initiation of ACTh therapy. There appeared to be no consistent difference in serum cortisol levels between patients receiving 20 units/day of ACTH and those receiving 30 or 40 units/day, and there was no difference in cortisol levels in those patients who became hypertensive and those who did not.