Fragments were isolated from subclones containing the insulin receptor cDNA described. Probe 1 as obtained from an SP64 subclone containing the 1011bp EcoRI fragment from the 5{prime} region of the U11rich cDNA. Probe 1 was a 677bp XhoI/EcoRI fragment from the {alpha} subunit region of the IR cDNA corresponding to nucleotides 334 to 1011, the putative ligand binding domain. Probe 2 was obtained from an SP64 subclone containing the 4190bp EcoRI fragment from the 3{prime} end of the U11rich cDNA. Probe 2 was a 1599 bp PstI fragment from the {beta} subunit region of the insulin receptor cDNA corresponding to nucleotides 2746 to 4345, encoding the tyrosine kinase domain. Segregation in at least one family was observed for the PstI, KpnI, and RsaI ({beta}) polymorphisms.