We investigated the effects and side effects of thyrotropin-releasing hormone (TRH) on severely epileptic children to evaluate the clinical usefulness of TRH in the treatment of epilepsy and compared them with the results of ACTH therapy. The subjects were 64 patients admitted consecutively between 1980 and 1986. Their seizures were frequent, more than one a day or more than one a week. The subjects were divided into two groups; 33 patients treated with ACTH and 31 treated with TRH. The mean follow-up periods in TRH and ACTH therapy were 8 months and 3.0 years, respectively. The daily dose of TRH-t 0.5-1 mg was administered intravenously (i.v.) or intramuscularly (i.m.) for 1-4 weeks. The follow-up periods were 3-12 months (mean 6 months). In the TRH group, complete control of seizures was achieved in 7 of 13 (53.7%) of those with infantile spasms, and marked improvement of EEGs were observed in 8 of 13 (61.5%) of them. In the ACTH group, seizure cessation was observed in 75% of infantile spasms. Of the patients who received ACTH, 66.7% had various side effects, including pneumonia, huge subcutaneous abscess, hypokalemia, cataracts, and brain shrinkage as shown on computed tomography (CT), whereas only 16.7% of the patients treated with TRH had transient reduction of urine volume without other laboratory and physical abnormalities. The results of the study indicated that some patients who received TRH had cessation of infantile spasms and improved EEG findings with no serious side effect. Because of the untoward side effects of ACTH therapy, TRH is considered a possible new treatment for children with infantile spasms.