A sensitive and selective analytical method for the enantioselective determination of terazosin in human plasma has been developed. The chromatography is based on the normal-phase chiral separation utilizing the analogue prazosin as the internal standard. The detection involves the direct introduction of the normal-phase eluent into an electrospray source followed by mass-selective detection. No pre-column derivatization was required prior to analysis. The chiral stationary phase used was Chiralpak AD 100 mm x 2.1 mm I.D. (10 microns particle size). The method was utilized to determine the concentrations of terazosin enantiomers in human subjects following a 5 mg single oral dose. Results were compared with those from an enantioselective HPLC-fluorescence method from the same subject plasma samples. The LC-MS results confirm with confidence that the two terazosin enantiomers have different elimination profiles.