Abstract: A sequencing method which exploits the thioacylation degradation of polypeptides and proteins is disclosed. The process involves reaction of the N-terminal amino acid of a polypeptide with an excess of a thioacylating reagent. After sufficient time to insure quantitative coupling and removal of excess reagent, the N-thioacyl polypeptide is subjected to cleavage by acid which affords a 2-substituted-5(4H)-thiazolinone of the N-terminal amino acid. Subsequent addition of a large excess of an aliphatic primary or secondary alcohol, either directly to the cleavage acid or after its removal, yields the corresponding N-thioacyl amino acid ester, a stable compound suitable for chromatographic separation and subsequent detection by contemporary methods of high pressure liquid chromatography.