Thyrotropin receptor (TSH-R), the main target for the autoantibody in Graves' disease, has been thought to be a thyroid-specific protein. However, we successfully obtained the cDNA fragments of TSH-R from rat retro-orbital tissues and adipose tissues by using polymerase chain reaction methods. Sequencing has revealed that the nucleotide sequence of the cDNAs from these non-thyroid tissues was identical to that from the thyroid. TSH-R peptide antibody, which recognizes rat TSH-R, stained a 104 kDa protein from the retro-orbital tissues and the adipose tissues. The band was not detected with the antibody preabsorbed with the peptide. These results suggest that the message is translated to make a TSH-R protein even in these non-thyroid tissues.