Recent technological advances in fiber optics, light sources, detectors, and molecular biology have stimulated development of numerous optical methods that promise to significantly improve our ability to evaluate human epithelium in vivo. These methods, collectively termed "optical biopsy," are nondestructive in situ assays of mucosal histopathology using light that can provide instantaneous tissue assessment. Narrow band imaging (NBI) is a novel technique that enhances the diagnostic capability of endoscopes in characterising tissues by using filters in a redgreenblue (RGB) sequential illumination system. This results in improved mucosal contrast and detail.