The amino acid sequence of the alpha subunit of rabbit (lagomorph) lutropin (lLH) has been determined. Overlapping peptides from trypsin and chymotrypsin digestions were isolated by reverse-phase high-pressure liquid chromatography (HPLC). Sequencing was by the dansyl-Edman procedure. Amide placements were established by HPLC analysis of the PTH amino acid derivatives. The proposed sequence of lLH alpha subunit is (asterisks denote carbohydrate attachment sites): This proposed sequence is highly homologous with the porcine, murine, ovine, and bovine glycoprotein hormone alpha subunit sequences. Two unusual proteolytic cleavages were observed: (1) a cleavage by trypsin between Asn-77 and Ala-78, and (2) a cleavage by chymotrypsin between Ala-45 and Arg-46. Similar enzymatic cleavages were previously reported for equine chorionic gonadotropin alpha subunit by Wardet al. and for these sites in the ovine LH alpha subunit by Liuet al. Chymotrypsin cleaved on the carboxyl side of methionine sulfone residues at positions 51 and 75.