Structural studies have substantiated the concept that the glycoprotein hormones consist of a "common" alpha subunit and "hormone-specific" beta subunit. Despite this, consensus is still lacking concerning certain portions of the amino acid sequences, including alignment of residues 81--82 in the alpha subunit. We have carried out sequence analysis of the alpha subunit of human luteinizing hormone (hLH) to clarify the assignment of these residues and to examine further the nature of the amino-terminal heterogeneity found among the different alpha subunits. Our structure showed residues 80--84 to be -His-Cys-Ser-Thy-Cys-, consistent with findings of others for human follicle stimulating hormone (hFSH) and human chorionic gonadotropin (hCG). The extensive degree of heterogeneity found in the amino terminal region of hFSH and hCG is present to only a minor extent in hLH. The differences in the pattern of amino-terminal heterogeneity among the various hormones may result from differences in the nature of cleavage of subunit from a larger intracellular precursor peptide.