The cloned renal porcine calcitonin (pCT) receptor cDNA expressed by transient transfection in COS-1 cells or stable transfection in HEK-293 cells was assayed for interaction with CT, amylin, and CT gene-related peptide. Both [ 125 I]salmon CT ([ 125 I]sCT) and [ 125 I]rat amylin displayed specific binding to transfected cells, and in both cases, pCT and rat amylin were equipotent in competing for binding. sCT was most potent in binding competition assays, whereas human CT and rat or human CT gene-related peptide did not compete. Despite the greater apparent affinity of sCT for receptor binding, sCT, pCT, and rat amylin had similar efficacies in stimulating the production of cAMP in the stably transfected cell line (EC50, 0.5-1.6 × 10 -9 M). These results contrasted with those obtained with the rat C1a CT receptor, for which amylin did not compete for [ 125 I]sCT binding and stimulated cAMP production only at high concentrations. These results show that pCT and amylin interact with similar potencies with the pCT receptor and suggest that amylin may act as a natural ligand for this receptor.