The ability of malignant tumor cells to form secondary lesions depends on multiple adhesive steps during invasion and metastasis. Details are given that a proteolytic treatment of the tumor cell surface causes a decreased attachment of the cells to matrix components. The attachment of murine B16 melanoma cells to the complete matrix (ECM) showed 40% inhibition after a bromelain treatment in comparison to control cells. A reduced binding rate to the isolated matrix components laminin and fibronectin was also found for the melanoma cell line as well as for a human bladder carcinoma (BC) after a proteolytic treatment with bromelain or ficin. Furthermore, the haptotactic migration of pancreatic carcinoma cells (DAN-G cell line) to laminin and fibronectin and that of B16-F1 cells to fibronectin was also influenced by ficin and bromelain, as shown in an in vitro invasion system. Other experiments were performed with arg-gly-asp-containing synthetic peptides (RGD polymer) as attachment protein mimicking the cell-binding domain of many adhesive proteins, which is recognized by several cell surface receptors. A bromelain treatment reduced the RGD attachment of B16 melanoma cells and that of their B16-F1 and B16-F10 variants, which differ in their capacity to colonize the lung. A panel of other proteases, including human elastase and plasmin, assayed in a physiological concentration, showed a similiar adhesion-reducing effect. The chromatogra-phic purification of bromelain resulted in fractions which only influenced the cell binding to the adhesive sequence in a lower extent than the starting material. The ability of the tested proteases to reduce the cell binding to the RGD polymer indicates an influence of the proteolytic treatment on the RGD-dependent integrin system. The findings support the possibility for a therapeutic use of proteases for adjuvant cancer treatment.