We propose that alpha-1-protease inhibitor (alpha 1 PI) can assume a major and beneficial role in preventing emphysema in alpha 1 PI-deficient individuals, and may also prove of value in the treatment of adult respiratory distress syndrome (ARDS). alpha 1 PI has a single, unusual disulfide bond that consists of a cysteine residue in the peptide chain covalently bound to a free amino acid cysteine. The linkage can be broken by reductants without adversely affecting the stability or the inhibitory activities of the protein. As a result of this property, alpha 1 PI can be effectively separated in solution from many other plasma proteins by salting out the contaminants in the presence of strong reductants. We have applied the technique of reductive-salting out, coupled with more conventional DEAE-anion exchange chromatography to isolate alpha 1 PI from Cohn Fraction IV-1, a relatively unused side product in the worldwide production of albumin and immunoglobulins. Furthermore, we have demonstrated that the product can be effectively pasteurized in the presence of various stabilizing additives. The necessary ingredients now exist for extensive clinical studies in the years ahead.