Peroxidase activity of inflammatory exudate collected from rats was studied in relation to the occurrence of leukocytes. The results proved that peroxidase activity correlates with the degadation rate of leukocytes, incresing activities were observed after breakdown of the cells with the aid of 1% Triton X‐100 and decreasing activities after neutropenia produced by cyclophosphamide. Ion exchange and molecular permeation chromatography as well as column and flat‐bed electrofocusing revealed heterogenic forms of exudate perodidases with pI values of 3.9–4.5, 5.7 and 7.2. Certain similarities with the peroxidases of human gingival exudate and rat inflammatory exudate were observed while human neutrophil myeloperoxidase seemed to have different characteristics. Leukocyte peroxidases are known to be antimicrobial against bacteria, fungi, viruses and mycop