PURPOSE: To compare the efficacy and tolerability of vigabatrin (VGB) and adrenocorticotrophic hormone (ACTH) as first-line therapy in infantile spasms. METHODS: Forty-two infants (22 males, 20 females) aged 2-9 months with newly diagnosed infantile spasms, were included in the trial. Patients were randomized to receive VGB 100-150 mg/kg/day or Depot ACTH 10 IU/day. The alternative drug was given if spasms were not controlled within 20 days or in cases of intolerance to initial therapy. Twenty-three patients (7 cryptogenic, 16 symptomatic) received VGB as first-line therapy; 19 patients (8 cryptogenic, 11 symptomatic) received ACTH as the first drug. RESULTS: Cessation of spasms was observed in 11 (48%) of the patients randomized to VGB and in 14 (74%) of those randomized to ACTH. Response to VGB was observed within 1-14 days, but two-thirds of patients (7/11) responded within 3 days. In the group treated with VGB, side effects such as drowsiness, hypotonia and irritability were observed in 13% of patients, compared with 37% in the group treated with ACTH. VGB was more effective than ACTH as treatment for cerebral malformations or tuberous sclerosis, whereas ACTH proved more effective in perinatal hypoxic/ischemic injury. The efficacy of the two drugs was similar in cryptogenic cases. Disappearance of interictal EEG abnormalities occurred sooner in patients randomized to ACTH than in those who received VGB as initial therapy. During the second phase, the alternative drug was given to the resistant patients. Spasms ceased in 2 of 5 patients treated with VGB and in 11 of 12 patients treated with ACTH. After 3 months, relapses of spasms were observed in 6 patients treated with ACTH and in 1 treated with VGB. VGB produced a therapeutic response in nearly half the patients receiving this drug. CONCLUSIONS: Our data lend further support to the view that VGB may be considered a first-choice drug in the treatment of IS.