(S)-Terazosin is a potent and selective antagonist of α-adrenoceptor with Ki values of 3.91 nM, 0.79 nM and 1.16 nM for α1a, α1b and α1d-adrenoceptor, respectively. It also has high-affinity for α2a, α2B and α2c-adrenoceptor with Ki values of 729 nM, 3.5 nM and 46.4 nM, respectively. It may prove to be a useful probe in understanding the functional role of subtypes of adrenoceptors in various tissues.