Human TSH receptor (hTSH-R) gene and RNA transcripts were analyzed by Southern and Northern blots in patients with various thyroid disorders, and in tissue cell lines. A 1.4 Kb cDNA encoding the extracellular human TSH-R domain was used as a probe. Southern analysis revealed two constant bands of 11.0 and 5.0 Kb (hTSH-R) in the thyroid and human white cell samples studied, regardless of the disease process. Northern analysis showed a predominant band at about 4.4 Kb in the thyroid tissues but not in non-thyroid tissue or cell lines tested. There were no gene rearrangements or abnormal transcripts in Graves' disease or multinodular goiter samples. In contrast, the labelled cDNA TSH-R probe did not bind to RNA isolated from 1 of 2 papillary cancer samples. A portion of the unique area of the h-TSH receptor (approximately nucleotides 1100-1230) was directly sequenced in thyroid glands from patients with Graves' disease, multinodular goiter, and differentiated thyroid cancer. No mutations or polymorphisms were identified in these samples, as compared to normal thyroid or control placenta, although further definition of sequence variation in other areas of the TSH receptor, as well as in more samples, needs to be performed. The present study indicates the normal patterns of DNA and RNA hybridization in a variety of thyroid tissues and disease states, and demonstrates that pathologic thyroid samples, with the possible exception of thyroid cancer, were not associated with specific nucleotide abnormalities in the unique area of the TSH receptor that was studied.