The authors describe their initial experience with a 2.8 mm (8.5F) fiberscope. The instrument, used to refine interventional radiology maneuvers of the intra- and extra-hepatic bile ducts, caused no additional discomfort to the 18 patients treated. The fiberscope permitted differentiation between different causes of biliary stenosis in the few cases where doubt persisted after percutaneous cholangiography. Brushing was also performed wherever necessary. The color, and thus the composition, of bile duct stones could also be determined. This has helped us to plan the therapy with methyl-tert-butyl-ether (MTBE) in patients with cholesterol stones. Compared with traditional fiberscopes (diameter of 5mm or more) the new instrument is easier to use, and allows more peripheral ducts to be reached, but is expensive and has a smaller field of view and fewer possibilities for therapeutic applications.