Five adult epileptic patients received 1,000 mg of valproic acid (Depakene) in both the regular and the enteric-coated form. Serum valproic acid levels were determined at suitable intervals after drug administration. Pharmacokinetic parameters were equivalent for both preparations except for an absorption lag with the enteric-coated form. The relative bioavailability of the two compounds was similar across the group of patients, although there were marked differences between individual subjects. Close supervision of valproic acid serum levels is suggested after a change in drug formulation.