Detection can be improved by the application of dyes which highlight more subtle abnormalities. This practice, known as chromoendoscopy (CE) is better than WLC at dysplasia detection but more time consuming for the patient and cannot guarantee that the whole colon is covered. CE has only been compared in clinical trials with standard definition endoscopy rather than the recently available high definition endoscopes with better resolution and picture. High definition (HD) endoscopy uses a high definition onitor and a high resolution CCD (charge coupled device) providing much better images than standard video endoscopy. HD colonoscopy promises therefore to provide an alternative to CE in UC surveillance without the need for the extra time and experience required for dye spraying for both endoscopists and nursing staff.