Immunohistochemical study of tissues from purulent wounds in rats after treatment with the collagenase isolated from the King crab Paralithodes camtschatica was undertaken. The enzymotherapy resulted in a rapid and efficient removal of necrotic debris. It was accompanied by fibrin elimination from the wound bed and subsequent formation of new capillaries. Cellular fibronectin with ED-A sequence was identified in the newly formed granulation tissue, which points to its active synthesis in situ. Polyclonal antibodies against two isozymes of the crab collagenolytic protease were obtained. By their use it was shown that, after application of the collagenase, both isozymes accumulated in fibrin deposits at the wound bed but did not penetrate adherent granulation tissue.