The in vivo bioavailability of magnesium valproate (500 and 1000 mg) enteric-coated tablets has been compared with that of sodium valproate (Depakine) (500 and 1000 mg) enteric-coated tablets. The two preparations were found to be bioequivalent; magnesium valproate appeared to be a drug without bioavailability problems and with reduced inter-subject variability, compared with that of sodium valproate. A reversed-phase HPLC method for the determination of valproates is described.