Sodium dodecyl sulphate polyacrylamide gel electrophoresis and reversed-phase high-performance liquid chromatography (HPLC) were used consecutively for the isolation of amyloid protein A (protein AA) from amyloid fibrils. Highly purified protein AA was obtained and determined by electrophoretic and amino acid analyses. The heterogeneity of protein AA was shown by HPLC. The isoforms of protein AA had different hydrophobicities, although they were equal in size and similar in amino acid composition. Compared with the conventional amyloid separation procedure (gel permeation chromatography), this technique is rapid, requires only small amounts of amyloid fibrils and may provide new information on amyloid proteins.