This study first is designed to see what dose of indigo carmine ingested orally mixed with the standard colonoscopy prep is needed to provide adequate staining of the right colon. It then will use this adequate staining concentration of Indigo Carmine to study whether this dye will increase the detection of polyps during colonoscopy.

Colon cancer occurs in 5% of the US population. Currently colon cancer screening is recommended at the age of 50 years old for all patients who are at average risk. Colonoscopy is considered the gold standard test for colon cancer screening. This is partly because colonoscopy not only can detect polyps which are cancer precursors but also can remove them, and thereby detecting cancer and its precursors and preventing cancer. Unfortunately recent data suggest that colonoscopy can miss a significant percentage of polyps, especially on the right side of the colon. It is thought that one of the major reasons for missing polyps in the right side of the colon is the fact that they are flat or sessile serrated adenoma, both of which are more difficult than protruding polyps to identify with ordinary colon preparation and colonoscopes. Chromoendoscopy is the application of dye during colonoscopy to enhance detection of polyps. It has been shown that it improves the detection of polyps and thus has the potential of improving the performance of colonoscopy and increasing the detection of these difficult to detect polyps. It is however cumbersome and time consuming, which has discouraged its use. Indigo carmine, one commonly used dye, is actually FDA approved as a food colorant and can be consumed orally. It is minimally absorbed. In addition it is used intravenously for diagnosis of injuries of the urinary system because it is very rapidly excreted by the kidneys. The investigators believe that taking it orally will be well tolerated, and that any of the dye that is absorbed will be rapidly excreted by the kidneys and thus quickly eliminated without any side effects. Effective staining of the colon with indigo carmine and increased detection of polyps could change the current standard of care for screening for colon cancer.

Inclusion criteria:

• Patients presenting for screening or surveillance colonoscopy
• Must be aged 50 to 75 yrs
• Must be able and willing to sign informed consent

Exclusion criteria:

• Known Creatinine >1.2
• Cirrhosis
• Pregnancy or breast feeding
• History of anaphylaxis to any dye
• History of bowel surgery or small bowel obstruction
• History of aspiration
• History of dysphagia
• American Society of Anesthesia class >2
• History of abnormal liver function test in the last year
• History of any degree of cytopenia in the last year