Abstract The pharmacokinetics of valpromide and valproic acid were investigated comparatively in 6 healthy subjects after intravenous administration of the two drugs. Valpromide was very rapidly and almost completely biotransformed to valproic acid (f m = 81.2 ± 10.5%; mean ± S.D.; n = 6). Relative to valproic acid valpromide has a very short half-life (0.84 ± 0.33 h) a high-clearance value (70 ± 30.5 l/h) and a large volume of distribution (V β = 75.3 ± 12.7 l). The results of this study showed that there was no significant difference between the biotransformation of valpromide to valproic acid after intravenous administration and that obtained after oral administration of valpromide. Therefore, in humans, valpromide appears to be a prodrug of valproic acid after intravenous as well as oral administration.