Of 196 children with febrile convulsions, 6.9 were placed on phenobarbital, 4-5 mg/kg/day b.i.d., and 32 on primidone, 15-20 mg/kg/day b.i.d. The remaining 95 children were given sodium valproate; the dosage was 20-25 mg/kg/day b.i.d. in 38 of them, 20-25 mg/kg/day t.i.d. in 24 of them, and 30 mg/kg/day b.i.d. in 33 patients. Recurrence rate of febrile convulsions during one year were not statistically different among these five groups. However, the dosage regimen of valproate of 20-25 mg/kg/day b.i.d. was relatively inferior to the other regimens of valproate in the prophylactic effect. This may be explained by the facts that when the same daily dosage of sodium valproate was given, the daily fluctuation of plasma levels was greater with the b.i.d.-regimen than with the t.i.d.-regimen, and that when the dosage interval was the same, the minimum plasma level of the day was lower with the smaller daily dosage regimen than with the larger one.