AbstractA method is described for distinguishing type I from type II muscle fibers and visualizing their motor endplates. Muscle biopsies from the region of the neuromuscular junction are snap frozen and sectioned on a cryostat. The sections are first incubated in a substrate containing beta nicotinamide adenine dinucleotide, reduced form, and nitroblue tetrazolium, then in a substrate containing alpha naphthyl acetate and hexazotized new feuchsin. This procedure takes only thirty-five minutes to do, no cholinesterase inhibitors are used, and both fiber type and neuromuscular junction are demonstrated simultaneously. It can be used routinely to help diagnose neuromuscular disorders and for myoneural research, in general.