In vitro transcription/translation, using rat thyrotropin receptor cDNA, results in the formation of nonglycosylated proteins able to bind thyrotropin, one of which approximates the 87 Kd size predicted for the receptor. In the presence of canine pancreatic microsomal membranes, putative glycosylation sites are modified as evidenced by digestion with endoglycosidase H. Using a deletion mutant, the presence of a hydrophobic peptide after the initiation signal is established as a signal peptide critical to post translational processing by the canine pancreatic membranes but not to binding thyrotropin.