SummaryBy using glass wool absorption followed by elution in strong salt solution and various precipitation methods and DEAE cellulose column chromatography, Hageman factor was purified from bovine plasma. Physico-chemical properties were studied in native protein and in 6 M urea (denatured) which was used in order to prevent monomer - polymer conversion. S°20,w was 7.07 in 0.1 M KC1 and 5.84 in 6 M urea. The intrinsic viscosity by Kragh’s method was 0.0540 ml/g inNaCl-phosphate buffer and 0.0815 ml/g in 6 M urea. Partial specific volume (v) by method based on amino acid residues in undenatured protein, was 0.724 cc/g. By using differential sedimentation equilibrium in 6 M urea-H20 and 6 M urea - D20 solution, v was determined as 0.740 cc/g. In urea, molecular weight (MW) was 142,000 as determined by meniscus depletion method. Similar values were obtained for nondenatured and denatured protein by Sephadex gel filtration, from amino acid composition using Brand’s method and Schachman’s equation. For undenatured and denatured Hageman factor, molar frictional ratios (f/fo) were 1.39 and 1.58, axial ratios were 5.0 and 7.0 and estimation of diffusion constant (D°20, w) based on S-rate, MW and v, gave values of 4.45 x 10-7 and 3.88 x 10-7 cm2/sec respectively. Our data indicate that the molecule was unfolded in 6 M urea solution. Two N-terminal groups, glycine and valine, were demonstrated by Edman procedure. Carbohydrate analysis revealed the following: hexosamine 0.8%, protein- bound hexose 1.9%, fucose 0.19% and sialic acid 0.35%. Isoelectric point was determined as 7.9 by electrofocussing technique. This protein migrated with gamma globulin on electrophoresis. Hageman factor was found to be a powerful immunogen. Anti Hageman factor reacted with both a plasma and a serum protein but not with purified IgG.