CAST and ELKS are major components of the presynaptic active zones of neurons in the central nervous system, but it remains elusive whether CAST and ELKS are also components of synapses in the peripheral nervous system. Here, we have attempted to examine their expression and localization at the synapses of neuromuscular junctions. Immunoreactivity for ELKS is partly colocalized with that for the major neuromuscular junctions marker alpha-bungarotoxin, which binds to acetylcholine receptors. Moreover, another active zone protein, Piccolo, is also present at neuromuscular junctions, together with ELKS, whereas CAST is not found. These results suggest that at least ELKS and Piccolo, but not CAST, are components of neuromuscular junction synapses in the peripheral nervous system.