A novel binding assay to kinin B1 receptors was developed, based on the design of a high-affinity agonist ligand, [125I]Tyr-Gly-Lys-Aca-Lys-des-Arg9-BK. Binding to rabbit aortic smooth muscle cells is highly temperature-dependent (optimal at 37 degrees C); apparent binding equilibrium is reached within 30 min, and competition by kinin analogs reveals the expected correlation with the B1 receptor pharmacology. The dissociation constant (Kd) of the labeled ligand is approx. 0.2 nM and this value does not change significantly as a function of cytokine pretreatment. However, the receptor abundance (Bmax) is significantly increased (1.5-fold) by pretreating the cells with interleukin-1 (IL-1), while oncostatin M (OSM) produces a marginal increase of the Bmax. This assay may be useful in documenting the regulation of B1 receptors in pathology.