A carboxyl-terminus microsequencing method has been developed on the basis of carboxypeptidase A digestion and derivatization of released amino acids with phenylisocyanate followed by subsequent high-performance liquid chromatographic analysis of the resulting phenylthiocarbamyl amino acids. This technique has been used to confirm the carboxyl-terminal sequence of bovine brain-derived acidic fibroblast growth factor. The method is of general application for the microsequencing of the carboxyl-termini of proteins. Since identification of derivatized amino acids was performed on the entire reaction mixture following digestion, a new chromatographic identification procedure for phenylthiocarbamyl amino acids was developed in order to resolve them from spurious peaks. This procedure can be applicable to amino acid analysis.