Abstract: The present invention relates to a liquid collagenase solution which will generate the pre-conditioning of the tissues covering peritoneal tumors by means of washing with said solution for a predetermined time and at a predetermined concentration for use as cytotoxic drug-enhancing or adjuvant treatment in the treatment of solid peritoneal tumors. Throughout the present invention, said solution will be used for administration to or for irrigating the tumor directly at a concentration and for a time such that it causes thinning of the mesothelial layer covering the intestinal tract without the involvement of intermediate or internal layers.