The bradykinin B1 receptor (B1R) is a cytokine-inducible G protein coupled receptor that inhibits mitogen-stimulated vascular smooth muscle cell proliferation at the late G1 phase of the cell cycle. The mechanism whereby the B1R inhibits cell cycle progression was investigated in cultured rat mesenteric arterial smooth muscle cells. Progression through the late G1 phase of the cell cycle requires upregulation of cyclin E that binds and activates cyclin dependent kinase 2 (Cdk2) leading to hyperphosphorylation of retinoblastoma protein (Rb). The B1R agonist, desArg9 bradykinin (DABK) was found to inhibit platelet-derived growth factor (PDGF)-mediated activation of cyclin E-Cdk2 and prevent hyperphosphorylation of Rb. DABK did not inhibit upregulation of cyclin E expression but increased expression of the Cdk2 inhibitor, p27Kip1 and the association of p27Kip1 with the cyclin E-Cdk2 complex. In addition, DABK inhibited the PDGF-stimulated expression of cyclin D that would otherwise siphon p27Kip1 away from inhibition of cyclin E-Cdk2. The signaling mechanism by which DABK regulated p27Kip1 was explored. DABK was found to stimulate the activity of MEK and ERK and prolong activation of MEK and ERK by PDGF. Inhibition of ERK activation using the MEK inhibitors, PD98059 and U0126 as well as the Src family kinase (SFK) inhibitor PP2, completely blocked the effect of DABK to increase p27Kip1 and partially reversed the DABK-mediated inhibition of PDGF-stimulated proliferation. These studies demonstrate that the B1R inhibits PDGF-stimulated mitogenesis in part by prolonged activation of ERK leading to increased expression of p27Kip1.