A zinc metalloendoprotease has been isolated from in vitro culture fluids of Trichuris suis adults. The protease was purified from total culture fluids by passage through a cation exchange high-pressure liquid chromatography column. The 45-kDa protease has a pH optimum of 7.0 and an isoelectric point of 8.0 and was localized to the stichosome of the parasites using immunohistochemistry techniques.