Saponins, which are present in plants, have been suggested as possible anticarcinogens. They possess surface-active characteristics that are due to the amphiphilic nature of their chemical structure. The proposed mechanisms of anticarcinogenic properties of saponins include direct cytotoxicity, immune-modulatory effects, bile acid binding and normalization of carcinogen-induced cell proliferation. However, the anticarcinogenic effects of saponins from commonly consumed plant foods have not been studied. Soybeans are one of the most important sources of dietary saponins. They are the main protein supplier in many vegetarian diets. Our results showed that soybean saponins at the concentration of 150-600 ppm had a dose-dependent growth inhibitory effect on human carcinoma cells (HCT-15). Viability was also significantly reduced. Soybean saponins did not increase cell membrane permeability in a dose-dependent fashion, whereas gypsophilla saponin, a nondietary saponin, increased permeability with increasing concentrations. Electron microscopy indicated that soybean and gysophilla saponins alter cell morphology and interact with the cell membrane in different ways.