A protocol of immunocytochemical demonstration of choline acetyltransferase (ChAT), a key enzyme of acetylcholine synthesis, in paraffin sections of the brain of some laboratory animals, is presented. The method is simple, gives fairly reproducible results and allows for demonstration of ChAT in neurons, nerve fibers, and terminals in preparations of at least three species of laboratory animals including rat, rabbit, and cat. Different kinds of fixation (10% formalin, 4% paraformaldehyde, or zinc-ethanol-formaldehyde) were found suitable for immunocytochemical visualization of ChAT, however, optimal results were obtained with the application of zinc-ethanol-formaldehyde