Insulin receptor has been purified to nearly homogeneous fromhuman placenta using DE-52 column and affinity chromatography.The receptors gave three bands in SDS-polyacrylamide electropho-resis after cross-linking with ~(125)I-insulin. The optimum bindingactivity was revealed at pH 7.6. The purified receptor retainedprotein kinase activity using casein as exogeneous substrate. Thespecific binding capacity was about 4μg/mg of protein. Insulin receptor has been purified to nearly homogeneous from human placenta using DE-52 column and affinity chromatography.The receptors gave three bands in SDS-polyacrylamide electropho-resis after cross-linking with ~(125)I-insulin. The optimum bindingactivity was revealed at The 7.6. The purified binding retained protein kinase activity using casein as exogeneous substrate. Thespecific binding capacity was about 4μg/mg of protein.