A means for casting step-gradients in linear polyacrylamide gel concentration for capillary electrophoresis is presented. A UV-Vis whole-column detector is used to profile the gel gradients cast in the capillary, while detection of fluorescein-labeled proteins is accomplished with an epi-illumination laser-induced fluorescence whole-column detection system. Fluorescence images of the capillary during the separation indicate a sharpening of the zones as they traverse the interface between gel concentrations. The potential of gel gradients in capillary electrophoresis for the analysis of wide molecular mass range protein or peptide samples is demonstrated. A mixture of proteins that range in molecular mass from 6 10 3 to 97.4 10 3 is separated in less than 15 min with baseline resolution of closely sized proteins that were not be resolved in a single concentration gel. Finally, analysis of several capillary images acquired during solute migration through the gel gradient permits the generation of a Ferguson plot from a single electrophoretic run.