The amino-acid sequence of human alpha 2-antiplasmin was determined by Edman degradation of peptides purified from CNBr, tryptic and chymotryptic digests. Of the total sequence of 452 amino acids of mature alpha 2-antiplasmin, as deduced from the cDNA sequence [Holmes et al. (1987) J. Biol. Chem. 262, 1659-1664], 444 residues were identified by amino-acid sequencing. Two differences were found between the peptide and cDNA analyses (Gly instead of Leu at position 10 and Gly instead of Ser at position 369). alpha 2-Antiplasmin contains two disulfide bridges (Cys64-Cys104 and Cys31-Cys113) and four glucosamine-based carbohydrate chains attached to Asn87, Asn256, Asn270 and Asn277. alpha 2-Antiplasmin is homologous with 12 other proteins belonging to the serine protease inhibitor (serpin) superfamily.