A growing body of evidence suggests an important contribution of the cellular actions of thrombin to thrombosis and restenosis following angioplasty. Recently we reported on SCH 79797 (N3-cyclopropyl-7-{[4-(1-methylethyl)phenyl]methyl}-7H-pyrrolo[3,2-f]quinazoline-1,3-diamine) and its analogs as new potent, nonpeptide thrombin receptor antagonists. This study further characterizes the biochemical and pharmacological actions of pyrroloquinazoline inhibitors of protease activated receptor-1 (PAR-1) in human platelets and coronary artery smooth muscle cells (hCASMC). SCH 79797 and its N-methyl analog (SCH 203099) inhibited binding of a high-affinity thrombin receptor-activating peptide ([³H]haTRAP, Ala-Phe(p-F)-Arg-ChA-HArg-[³H]Tyr-NH₂) to PAR-1 with ic₅₀ values of 70 and 45 nM, respectively. SCH 79797 inhibited [³H]haTRAP binding in a competitive manner. SCH 79797 and SCH 203099 inhibited α-thrombin- and haTRAP-induced aggregation of human platelets, but did not inhibit human platelet aggregation induced by the tethered ligand agonist for protease-activated receptor-4 (PAR-4), γ-thrombin, ADP, or collagen. SCH 203099 inhibited surface expression of P-selectin induced by haTRAP and thrombin, and it did not increase P-selectin expression or prevent thrombin cleavage of the receptor. Thrombin and TFLLRNPNDK-NH₂ (TK), a PAR-1-selective agonist, produced transient increases in cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) in hCASMC. This increase in [Ca²⁺]_i was inhibited effectively by SCH 79797. However, the Ca²⁺ transients induced by SLIGKV-NH_2, a PAR-2-selective agonist, were not inhibited by SCH 79797. Thrombin- and TK-stimulated [³H]thymidine incorporation also was inhibited completely by SCH 79797. The results of this study demonstrate that SCH 79797 and SCH 203099 are potent, selective antagonists of PAR-1 in human platelets and hCASMC. These data also suggest that the thrombin stimulation of Ca²⁺ transients and mitogenesis in hCASMC is mediated primarily through activation of PAR-1.