Patients 18 years of age and older who have had ulcerative colitis for at least 4 months may be eligible for this study. Candidates will be screened with a review of their medical records, a medical history and physical examination, electrocardiogram (EKG), blood, urine, and stool tests, and a pregnancy test for women of childbearing potential. A colonoscopy will also be done to determine disease activity and extent. This test uses a lighted tube to examine the amount of inflammation in the colon and take tissue samples (biopsies) for testing. Before the test, the patient is given a medicine to allay anxiety and the discomfort of inserting the endoscope into the rectum. This flexible tube allows the doctor to see the intestinal mucosa and project an image of the inner lining of the intestine onto a TV monitor. At various places in the intestine, small pieces of tissue are plucked out by a special device at the tip of the endoscope. The procedure generally lasts 30 minutes to 1 hour.