Patients with stage III and IV cancers of different sites revealed a 47-76% increase in serum total antitrypsinic activity. A mean 40% increase was observed in cases of inflammatory pathology. Both study groups demonstrated raised alpha 1-antitrypsin levels, while that of alpha 2-macroglobulin did not show any significant changes. The level of alpha 1-antitrypsin accounted for 89 and 83% of total antitrypsinic activity in cases of inflammation and controls, respectively, while in cancer patients this index was significantly lower (70%). The diagnostic value of total antitrypsinic activity appeared to be higher than that of alpha 1-antitrypsin level determination. It is inferred that, apart from alpha 1-antitrypsin, malignant growth is associated with raised levels of more specific endogenous proteinase inhibitors, except alpha 2-macroglobulin.