Dimethylhydrazine-induced and azoxymethane-induced carcinomas of the colon will be studied with respect to the kinetics of RNA and DNA accumulation and of cell proliferation as they are potentiated by supranormal cell proliferation produced by several experimental models. These are distal small-bowel resection and bypass, proximal small-bowel resection and bypass, transplantation of the papilla of Vater more distal in the bowel, and transposition of the colon. In addition the possible tropic or permissive action of gastrin will be observed. Azathioprine will be used as a reversible suppressor of DNA synthesis.