A HPLC procedure was developed and validated for determining nanogram per milliliter concentrations of the dual 5alpha-reductase inhibitor PNU 157706 in rat plasma. The compound was extracted from plasma with diethyl ether followed by purification using a CN cartridge. The chromatographic separation was performed with a C18 column using a water-acetonitrile-methanol mixture as eluent. UV detection at 210 nm was used for the quantification of the compound over the concentration range 5-500 ng/ml plasma. The method has a lower limit of quantification of 5 ng/ml and good precision and accuracy. This method has performed well during analysis of several toxicokinetic and pharmacokinetic studies in the rat.