We developed a rapid and efficient method to achieve good penetration of anti-tyrosine hydroxylase (TH) antiserum into whole mounted rat retinas. The retinas were defatted before incubation in the primary antibody. This operation was thought to increase membrane permeability, facilitating penetration of antibodies. As a result, all TH-positive cells in the entire retina were labeled. Thus, it becomes possible to study the morphology, the distribution, and the counting of TH immunoreactive cells in whole retinas.