Since the success in chemical induction of cancer in rabbit's ear skin by K. Yamagiwa in 1915, oncologists of the world have come to believe that they can only solve their problems by means of animal experimen tation. The importance of environmental factors became moreevident in 1935 when T. Yoshida and T. Sasaki introduced azodye hepatocarcino genesis in rats. In the domain of the gastrointestinal tract, T. Sugimura has more recently accumulated enough evidence to indicate that locally active chemical mutagens are carcinogenic. In contrast, principal approaches to colorectal tumors have been...