We have adapted a new, high-performance magnifying fibercolonoscope (FCS-ML II) developed by Machida Industries, for clinical use. We have observed the remission process of ulcerative colitis with this new instrument and have compared our findings with those obtained by clinical examination, X-ray, ordinary gastroscope, and histologic examination of biopsy specimens. Our results show that the findings of magnifying fiber-colonoscopy correspond to those obtained with biopsy and histology, indicating that this new instrument promises to be a highly effective tool for the accurate assessment of the degree of remission of ulcerative colitis.