Calcitonin (CT), the hypocalcemic hypophosphatemic hormone, is present in many vertebrate species. The principal target organs for CT are, in mammals, kidney and bone, and in fish, bone and gill. We have investigated the presence of renal calcitonin binding sites in a fish (Salmo gairdneri), two amphibians (Bufo bufo and Rana esculenta), two reptiles (Pseudemys scripta and Gekko gecko), and two birds (Gallus domesticus and Cothurnix japonica). We compared their distribution to a mammal, the rat (Wistar strain), using quantitative autoradiography methods. Moreover, CT binding sites were also characterized in the chicken kidney by a membrane assay. No renal 125I-sCT binding sites were detected in the fish, the amphibians, and the reptiles studied. In the rat, binding sites were present in the outer medulla and in the cortex. In the chicken and in the quail, scattered binding sites were also observed in the medulla and in the cortex, whose pattern seemed to follow the distribution of the glomeruli and/or the collecting tubules. Chicken kidney membranes were also purified by sucrose gradient centrifugation. Scatchard analysis of the binding data revealed the presence of one type of 125I-sCT binding site with an apparent dissociation constant of 4.3 nM and a number of sites of 73 fmol/mg/protein. The present results suggest that calcitonin renal receptors appeared late in evolution and thus that a regulation of renal function by calcitonin was only effective in birds.