Conformational transitions of HAFP in the pH-range 2-12 were studied by fluorescence spectroscopy, fluorescence polarization measurements, circular dichroism and hydrophobic chromatography in order to compare molecular architecture of HAFP and that of human serum albumin. It was found that HAFP has a remarkably hydrophilic exposed molecular surface at neutral pH and possesses extensive hydrophobic binding sites located in crevices. Conformational changes occur in HAFP in the acid and alkaline pH regions; extensive hydrophobic areas in HAFP are exposed by both acid and alkaline transitions. The alpha-helix contents of HAFP were determined as 67% at pH 7.6, 47% at pH 2.11.