A simple method for determining the concentration of astilbin, a flavanone, in rabbit plasma has been developed. After liquid-liquid extraction, the flavanone was detected by HPLC on a 4.6-microm octadecylsilica column (Nova-Pak C-18) at 291 nm. Linear calibration graphs for astilbin were constructed from 0.44 to 22.17 microM. The limit of quantitation was 0.44 microM in plasma. The method has been applied to pharmacokinetic studies after a single i.v. and an oral administration of the compound to rabbits.