A method for purifying α-1 proteinase inhibitor from an aqueous solution containing α-1 proteinase inhibitor, comprising the steps of: (a) removing a portion of contaminating proteins from the aqueous solution to obtain a purified solution containing α-1 proteinase inhibitor, wherein said removing step comprises the steps of (i) precipitating said portion of contaminating proteins from said aqueous solution by adding a polyethylene glycol with a MW between about 3,000 and about 4000 to said aqueous solution at a concentration between about 3% to 15% weight per volume, and adjusting the pH of said aqueous solution from about 5.0 to about 6.0; and (ii) separating said precipitated portion of contaminating proteins from said aqueous solution, thereby obtaining said purified solution containing α-1 proteinase inhibitor; then (b) diluting said purified solution to reduce the conductivity of said purified solution so that α-1 proteinase inhibitor binds to an anion exchange resin; then (c) passing said purified solution through an anion exchange resin so that α-1 proteinase inhibitor binds to said anion exchange resin; then (d) eluting α-1 proteinase inhibitor from said anion exchange resin to obtain an eluted solution containing α-1 proteinase inhibitor; then (e) adjusting the pH, conductivity and protein concentration of said eluted solution containing α-1 proteinase inhibitor so that α-1 proteinase inhibitor does not bind to a cation exchange resin; (f) passing the eluted solution through a cation exchange resin; and (g) collecting a flow-through from said cation exchange resin that contains α-1 proteinase inhibitor. (a) removing a portion of contaminating proteins from the aqueous solution to obtain a purified solution containing α-1 proteinase inhibitor, wherein said removing step comprises the steps of (i) precipitating said portion of contaminating proteins from said aqueous solution by adding a polyethylene glycol with a MW between about 3,000 and about 4000 to said aqueous solution at a concentration between about 3% to 15% weight per volume, and adjusting the pH of said aqueous solution from about 5.0 to about 6.0; and (ii) separating said precipitated portion of contaminating proteins from said aqueous solution, thereby obtaining said purified solution containing α-1 proteinase inhibitor; then (i) precipitating said portion of contaminating proteins from said aqueous solution by adding a polyethylene glycol with a MW between about 3,000 and about 4000 to said aqueous solution at a concentration between about 3% to 15% weight per volume, and adjusting the pH of said aqueous solution from about 5.0 to about 6.0; and (ii) separating said precipitated portion of contaminating proteins from said aqueous solution, thereby obtaining said purified solution containing α-1 proteinase inhibitor; then (b) diluting said purified solution to reduce the conductivity of said purified solution so that α-1 proteinase inhibitor binds to an anion exchange resin; then (c) passing said purified solution through an anion exchange resin so that α-1 proteinase inhibitor binds to said anion exchange resin; then (d) eluting α-1 proteinase inhibitor from said anion exchange resin to obtain an eluted solution containing α-1 proteinase inhibitor; then (e) adjusting the pH, conductivity and protein concentration of said eluted solution containing α-1 proteinase inhibitor so that α-1 proteinase inhibitor does not bind to a cation exchange resin; (f) passing the eluted solution through a cation exchange resin; and (g) collecting a flow-through from said cation exchange resin that contains α-1 proteinase inhibitor.