• The clinical anticonvulsant efficacy of once-daily administration of phenobarbital sodium was evaluated in 29 adults with head injuries. All patients were initially well controlled, with therapeutic blood levels of phenobarbital obtained from divided dose regimens, ranging from two to four daily administrations. All therapies were then converted to once-daily administration of the total dose at bedtime. Twenty-six patients (93%) remained with-in normal therapeutic blood levels without any dose change. Phenobarbital can safely, and perhaps should, be administered in a once-a-day regimen, with resultant benefits of probable increased compliance and decreased daytime sedation, if administered at bedtime.