Activity of prolyl endopeptidase (EC 3.4.21.26) which hydrolyses the Pro⁷‐Phe⁸ bond in angiotensin II has been found to elevate in experimentally produced granulomatous inflammation in liver and skin. We purified the enzyme 1,536‐fold by 6 steps from murine hepatic granulomas. The purified enzyme has a molecular weight of 79 kDa and physiocochemical properties equivalent to those previously reported for prolyl endopeptidase purified from other sources. By HPLC analysis, the cleavage of Phe⁸‐Leu¹⁰ and Phe⁸ from angiotensin I and II, respectively, was detected and quantified. Monospecific IgG was prepared from serum of rabbits injected with purified enzyme. Concentration of the enzyme was immunohistochemically detected in cells which form granulomatous organization, but not in inflammatory cells surrounding the foci. The antibody, however, cross reacted with the enzyme in adjacent liver cells and weakly stained their cytoplasm. The findings indicate that this enzyme, in addition to angiotensin converting enzyme, may serve as a useful biochemical marker for granulomatous tissue reactions.