Binding of IGF-I to plasma membranes from bovine mesenteric arteries was studied. The maximal specific binding of IGF-I was found to be 7.4 +/- 1.7% of total 125I-IGF-I added to the incubation medium. Unlabelled IGF-I displaced 125I-IGF-I with an IC50 value of 0.5 nmol/l and a maximal displacement of 64.2 +/- 2.8% of total binding. The potency of insulin to displace 125I-IGF-I was 100-1000-fold lower. Cross-linking of 125I-IGF-I to the receptor with disuccinimidyl suberate, followed by SDS-polyacrylamide gel electrophoresis under reducing conditions showed an IGF-I binding protein with a molecular weight of 146,000 Dalton. In summary, we have shown the presence of receptors for IGF-I in plasma membranes isolated from macrovessels. The binding characteristics and the size of the binding unit were found to be similar to those of the IGF-I receptor found in cultured vascular smooth muscle cells. Furthermore, insulin at high concentrations was found to interact with the IGF-I receptor.