We have performed experiments to determine whether the soybean-derived protease inhibitor, Bowman-Birk inhibitor (BBI), has the ability to affect intestinal carcinogenesis in Min mice. Min mice have an autosomally dominantly inherited predisposition to multiple intestinal neoplasms and are known to have a very high spontaneous rate of tumor development in both the small intestine and colon. BBI was administered in the diet as BBI Concentrate (BBIC), the form of BBI which is currently being evaluated in human trials as a cancer chemopreventive agent. We observed that 0.5% dietary BBIC led to a 42-50% reduction in the number of tumors/mouse in the small intestine and colon and a 41% reduction of tumorigenesis in the colon when the data are analyzed in terms of the fraction of mice bearing tumors. Thus, tumor-development in both the small intestine and colon of Min mice can be significantly suppressed by BBIC, despite the fact that the animals carry a predisposing mutation that leads to a markedly increased intestinal tumor incidence and mortality rate.