This study was aimed at testing the efficacy and innocuousness of a single dose of sodium valproate (SV) for the treatment of epilepsy, as compared with 3 daily doses. It was tested on 35 children, 5 to 15 years of age, presenting with the idiopathic form of generalized epilepsy. At the end of one year of treatment with 20 mg/kg/day of SV in 3 daily doses, the children were given a single dose at 8 PM daily. Every 3 months for a period of one year, patients were examined in order to monitor the clinical efficacy and side effects, liver function tests and serum levels of SV at 9 AM and 6 PM. Twenty patients who were well controlled with 3 daily doses had no fits with the single dose treatment. Ten patients, who had had one fit every 6 months during the observation year had no convulsions during the year on a single dose: however, 5 others who had had one fit every 6 months with 3 doses, had fits with the same frequency with the single dose treatment. There were no side effects. SV plasma levels at 9 AM were always higher than those at 6 PM. The efficacy of a single dose may result from the action of SV which increases the intra-cerebral levels of GABA, which are delayed and prolonged.