α-Adrenergic receptors (α-ARs) are important targets for drug design due to their roles in various physiological events. Prior studies using cloned human α-AR assay systems identified that the α1-AR mediating human prostatic smooth muscle tone is the α1a-AR subtype. Here, we report the use of these systems to discover α1a-AR-specific antagonists. Cell membrane preparations from cell lines expressing cloned human α1 (α1a, α1b, α1d) and α2 (α2a, α2b, α2c) ARs were used in radioligand displacement experiments. The 1,4-dihydropyridine (S)-(+)-niguldipine showed 340- and 630-fold selectivity for α1a-AR over α1b- and α1d-ARs, with high affinity (Ki = 0.2 nM). Analogs 8 (4-(4-nitrophenyl) analog) and 9 (amide-linked analog, SNAP 5089) were synthesized. Compound 8 maintained high α1a-AR affinity and selectivity with reduced calcium channel affinity. Compound 9 exhibited even better binding profiles: Ki = 0.4 nM for α1a-AR, 630-, 1500-, and 1500-fold selectivity over α1b-AR, α1d-AR, and L-type calcium channel, respectively, and >1000-fold selectivity over α2-ARs. Functional studies showed neither 8 nor 9 acted as agonists at 1 μM, but both inhibited norepinephrine-induced calcium responses in α1a-AR-transfected cells (95% inhibition) more potently than in α1b- (30%) or α1d- (20%) AR cells. The (-)-enantiomer of 9 was more active at α1a-AR but less active at the calcium channel than the (+)-enantiomer. In summary, we discovered the first subtype-selective α1a-AR antagonists. Compounds 8 and 9 will aid in α1-AR localization/functional studies and drug design for disorders like benign prostatic hyperplasia (BPH).