The isoelectric banding patterns of three commercial carrier ampholytes (pH range 2-11) were visualized in both Sephadex gel slabs and on paper prints, by means of ultraviolet light. 2. The fluorescence pattern of Servalyt is described in detail. This pattern, which has sharply delineated bands, is characteristic, and is reproducible from run to run with different batches of Servalyt. A total of 56 fluorescent bands were identified on gel slabs, and 62 on prints. 3. Methods are described for identifying individual fluorescent bands on prints. A classification scheme for organizing the banding pattern of Servalyt and naming individual bands is presented. 4. On gel slabs and on prints, the fluorescent pattern of a carrier ampholyte may be used analytically as a map for the location and identification of focused protein bands. The utility of the fluorescent pattern for characterising commercial ampholyte mixtures is discussed. 5. Individual fluorescent bands on the gel slab have characteristic pH values, which are constant from run to run and remain constant in the presence of focused sample proteins. On prints, these bands serve as permanent internal markers for assigning isoelectric points to protein bands.