The binding of mouse hybridoma monoclonal antibodies directed against human colon carcinomas was studied using an ex vivo perfusion model of a freshly resected human colon segment containing a carcinoma. Tumor and the surrounding normal bowel is exposed to the putative tumor antigen through an intact vascular system without mechanical or enzymatic cellular alteration. An hour of perfusion was conducted on thirty specimens using five different monoclonal anticolorectal cancer (ACRC) antibodies. Three were gamma 1, one gamma 2A and one was IgM isotype. Control anti-influenza virus monoclonal antibodies were used to demonstrate absence of nonspecific binding. Our antibody 17-1A bound to the colon cancer in seven of ten trials, but bound to normal colon cells also in four of these trials. The IgM antibody did not bind to anything. The two gamma 1 antibodies that recognize an antigen shed from the surface of the cell did not demonstrate cell binding under conditions of this study, and conditions to detect this will have to be modified. The ex vivo perfusion model as performed in this study can provide a valuable adjunct to evaluate the potential clinical utility for antibody conjugate radiolocalization or therapy of colon cancer.