The wild type murine luteinizing hormone (mLH) receptor, which in its mature form is predicted to be a protein of 674 amino acids (mLHR), and an artificially mutated form lacking the last 46 amino acids (mLHR-ct628) were stably expressed in murine L cells. Both forms stimulated adenylyl cyclase and underwent rapid desensitization. The mutation removed 1 tyrosine, 2 threonines, and 6 serines from the receptor. The results indicate that none of these potential phosphorylation sites participates in either adenylyl cyclase stimulation or receptor desensitization. Our results with the mLHR-ct628 (carboxyl-terminal amino acid sequence CCKHRAEL) differ from those reported recently for the essentially identically mutated rat LHR that lacks the last 43 amino acids (rLHR-ct631 with carboxyl-terminal amino acid composition CCKRRAELYRR). This 43-amino acid truncation was described to have the effect of preventing hormone-induced desensitization. While the reasons for the discrepant results are not known, our results do not support the proposal for a participatory role of the extreme carboxyl terminus of the receptor in its desensitization.