Fractionation into several individual components was achieved from Cohn's Fraction III of human plasma by the successive application of separation principles that depend on solubility, charge, and size (precipitation, ion-exchange chromatography, and molecular-sieve chromatography methods). Characterization was made by various electrophoretic procedures such as microzone on cellulose acetate, disc on acrylamide gel, and immunoelectrophoresis, and includes some physicochemical properties of the purified proteins. There are found to be various components of γ-globulins, α2-macroglobulins, β-glycoproteins, β-lipoproteins, and other minor proteins in Cohn's Fraction III of normal human plasma. The physicochemical properties of two γA-globulins and two α2-macroglobulins were investigated.