Purified rat .alpha.1-antitrypsin and albumin were radiolabeled, and their distribution and catabolism in various tissues were studied in rats with inflammatory granuloma or transplanted sarcoma. I.v. administered labeled .alpha.1-antitrypsin accumulated remarkably in extravascular spaces of the granuloma or sarcoma tissues. Among the normal organs examined, the lung preferentially incorporated .alpha.1-antitrypsin. Most of the .alpha.1-antitrypsin accumulated in these 3 tissues remained in a TCA[trichloroacetic acid]-precipitable form throughout the observation period. Since .alpha.1-antitrypsin is incorporated in large amounts into inflammatory or tumor tissues, it could play a role in regulation of inflammatory processes or control of tumor proliferation. Studies on TCA fractionation also suggest that liver and kidney provide the main sites for degradation of this protein. Although the accumulation of labeled albumin in granuloma and sarcoma was less marked, it showed the same distribution and degradation pattern as .alpha.1-antitrypsin in both morbid states.