The determination of the tryptic peptide mapping of sequence 1-298 of human serum albumin (HSA) by chemical and enzymatic cleavage and combined use of high-performance liquid chromatography (HPLC) and fast-atom bombardment mass spectrometry (FAB-MS) is described. A total coverage of about 75% of the entire sequence was obtained. Unidentified fragments included some peptides which were not present in the chromatograms because of their extreme hydrophobic or hydrophilic character, as indicated by the calculated retention times. Due to the high reproducibility of the experiments and to the satisfactory yield of the tryptic fragments identified, the combined use of HPLC and FAB-MS appears to possess great potential for structural investigation of HSA.