Localization of calcium-activated neutral protease in normal monkey (Cebus apella) skeletal muscle and peripheral nerve was studied by application of the indirect immunofluorescent and peroxidase-antiperoxidase techniques for light and electron microscopy. In muscle, the protease was demonstrated in association with endomysial collagen fibrils, basal lamina, sarcolemma, and Z-bands and also at neuromuscular junctions. In nerve, the enzyme was demonstrated in association with endoneurial collagen fibrils, basal lamina, axolemma, and neurofilaments of both myelinated and unmyelinated axons. Intramuscular injections of the thiol protease inhibitor, leupeptin, abolished Ca-activated neutral protease immunoreactivity in both muscle and peripheral nerve. These data suggest that the protease is localized both intracellularly and extracellularly in normal primate muscle and peripheral nerve. Inhibition of basal lamina associated neutral protease by leupeptin after denervation may hold significance for protecting this structure against degradation and preserving it as a neurotrophic lattice for axon regeneration.