Dispensing subcutaneously 1,2-dimethylhydrazine, intestinal carcinogenesis was investigated in male Fisher rats with different surgical colonic anastomoses, producing blind gut loops of isoperistaltic high (fecal stasis) and anisoperistaltic low fecal contact. One hundred and eight rats, except 1 rat of the control group, developed colonic neoplasms. In contrast to the control group, mainly in anastomotic areas and in isoperistaltic blind gut loops with intensive fecal contact huge adenocarcinomas of exophytic growth appeared with a mean tumor diameter (MTD) of 1.9 ± 0.7 to 2.2 ± 0.8 cm. Even in the control group, where rats only underwent laparotomy, we observed small polypoid adenocarcinomas mainly located in the distal colon (MTD: 0.7 ± 0.3 cm). Anastomotic areas and isoperistaltic blind loops with intensive fecal contact proved to be regions with a higher risk for carcinoma formati