The changes in the intestinal microflora were examined in patients with advanced carcinoma of the large intestine, and healthy subjects were surved as control. Comparing to control, patients group revealed high fecal moisture and fecal pH, but showed low levels in various organic acids except succinic acid. Only succinic acid was detected in high level and frequency. No significant difference in the number and occupation rate of Gram-positive bacteria participating in the endogenous endotoxin production was noted between both groups. The pattern of fecal microflora in patients group was similar to that in control. However, the aerobic microorganisms including Staphylococcus were highly found in patients group. These results suggested that the colonic enviornment of the patients with large bowel carcinoma was in aerobic state in comparison with healthy subjects.