The biotin-XX conjugate of the anti-lucifer yellow, rabbit IgG antibody was developed to overcome certain limitations of the Lucifer yellow dye, which is frequently employed as a polar tracer for neuronal cell labeling. Even though the cell soma of a lucifer yellow-filled neuron may be brightly stained, its finer processes can sometimes be faint and may fade rapidly or be obscured by the more intensely stained portions of the neuron. By using anti-lucifer yellow dye antibodies in conjunction with standard enzyme-mediated immunohistochemical methods one can develop a more permanent, fade-free signal for light microscopy.