From January 1976 to May 1980, patients presenting overt rectal bleeding or taking fecal occult blood testing included 38 with early colorectal carcinoma treated surgically or endoscopically and 42 with colorectal adenoma excised endoscopically. Of 38 patients with early carcinoma, 22 presented overt rectal bleeding and in 14 the test was positive and in 2 was negative Thus, the overt and or occult bleeding was noted in 95% of 38 patients. Of 42 patients with adenoma, 16 presented overt bleeding, and 20 showed positive and 6 negative respectively. Thus, overt and/or occult bleeding was noted in 86% of patients with adenoma excised endoscopically.The incidence of overt bleeding increased with size in early carcinoma, but was poorly correlated with the size of adenoma.With regard to the location of early carcinoma, overt bleeding was extremely common in rectal tumor and was seen approximately in a half of patients with sigmoid tumor. Adenomas with negative fecal occult blood testing were located mainly proximal to the sigmoid colon. The sigmoid colon has a tendency to bleed easily when rubbed with feces passing through a narrow lumen. Regarding to the shape, overt rectal bleeding was more commonly seen in pedunculated adenoma and sessile early carcinoma. All of 18 carcinomas with submucosal involvement (sm carcinoma) demonstrated either overt or occult bleeding. Only 2 of 20 patients with intramucosal carcinoma (m carcinoma) had negative fecal occult blood testing. Carcinoma without adenomatous component was similar to sm carcinoma regarding to the pattern of bleeding. In contrast, carcinoma in adenoma was similar to adenoma in this respect. In adenoma, no significant correlation was noted between bleeding and severity of histological atypism.