However, some studies have shown that the sensitivity for the detection of dysplasia during colonoscopy in patients with ulcerative colitis can significantly be enhanced by using chromo-endoscopy. These studies used methylene blue or indigo carmine as a contrast agent with or without high magnification endoscopy. Chromo-endoscopy guided targeted biopsies significantly reduced the number of biopsies for each procedure and detected more neoplastic lesions. It was therefore concluded that colonoscopy with chromo-endoscopy guided biopsies is more efficient and cost saving. Chromo-endoscopy with targeted biopsies is an alternative to white light endoscopy with random biopsies every 10cm. The European Crohn and Colitis association now suggests that the use of methylene blue or indigo carmine chromoendoscopy is an alternative to random biopsies for appropriately trained endoscopists and is superior to random biopsies in the detection rate of neoplastic lesions In this study we want to compare chromoendoscopy with targeted biopsies as the gold standard with new new endoscopic image techniques called virtual chromoendoscopy.