We screened a human thyroid cDNA library with two synthetic oligonucleotides based on the reported amino acid sequence of the 3rd and 4th transmembrane domains of a putative human TSH receptor and related receptors. The nucleotide sequence of a 4 kb clone revealed an open reading frame of 764 amino acids (86,816 Daltons) with a putative signal peptide, seven transmembrane domains, five potential glycosylation sites, and a very short intracytoplasmic region. Homology with the extracellular domain of the pig LH/CG receptor was only 33%. Chinese hamster ovary cells stably transfected with this cDNA in an expression vector generated a functional receptor, able to activate adenylate cyclase, specifically in response to TSH stimulation.