Blood in the stool with pus is an indication of an infection or inflammation in the intestine, and an indication that the lesion is in the colon or rectum and not in the small intestine. Pus and blood in the stool is due to erosion of the intestinal mucosa and can be caused by infectious or non-infectious factors. The most common infectious factor is dysentery, while other bacterial infections or parasites can sometimes cause pus and blood in the stool. Among the non-infectious factors, ulcerative colitis and Crohn’s disease are the most common, while colon polyps, rectal polyps and malignant tumors may also cause pus and blood in the stool after necrosis and secondary infection.