In order to improve the detection of flat urothelial neoplasia an improvement in optical methods might be helpful. We investigated the use of confocal laser scanning microscopy in a pilot study of specimens with bladder cancer. A total of 35 fresh ex vivo specimens of 20 human bladders of patients who underwent radical cystectomy were examined with a modified confocal laser scanning microscope (670 nm). The field size was 200x200 microm and tissue was investigated up to depths of 120 microm. Resulting data sets were reconstructed three-dimensionally by computer software. Results were compared with conventional histology. Microscopically diseased bladder mucosa showed cytological and histological criteria of malignancy which were readily identifiable by laser scanning microscopy. In all cases we were able to detect the presence of malignancy with the images generated by the confocal laser scanning technique. Atypical cellular structures and subepithelial hypervascularization were prominent features. Carcinoma in situ lesions could also be identified in many cases. Confocal laser scanning microscopy allows the analysis of cellular and epithelial architecture of the urothelium in a detail which is beyond the limitations of conventional endoscopy by white light cystoscopy. Therefore, the principle would probably be of benefit if the technical limitations can be overcome.