1.Age 30 years old or above, with unexplained blood in stool, irregular stool, change in stool habit or shape; 2.Unspecified chronic diarrhea or long-term chronic constipation; 3.Unspecified anemia and wasting; 4.Family history of colorectal cancer; 5.Persons who have suffered from colon polyps, colon cancer or ulcerative colitis; 6.Abdominal masses, especially lower abdominal masses need further definite diagnosis 7.Follow-up examination after colon and rectal surgery.