Gastrodia elata (GE) is an oriental medicinal herb which has been used traditionally for the treatment of various brain diseases including convulsion and epilepsy. The purpose of this study was to determine pharmacokinetic parameters of 4-hydroxy-3-methoxybenzaldehyde (HMBA) and p-hydroxybenzaldehyde (PHBA), constituents of GE, in rats. Male rats were cannulated in the femoral vein, femoral artery, bile duct and ureter. They received a single i.v. bolus dose of either HMBA or PHBA through the femoral vein. The concentration of HMBA or PHBA in plasma, bile and urine samples were analyzed by reversed-phase HPLC. HMBA and PHBA have very short half-lives, i.e. 4.03 and 2.26 minutes respectively. Most of HMBA and PHBA were thought to be eliminated through metabolism as the metabolized fraction approaches unity. Derivatives of HMBA or PHBA with longer biological half-lives should be designed to develop better anticonvulsants and more complete qualitative and quantitative understanding of the overall pharmacokinetic fate of these compounds awaits further investigation.