The existence of neuronal nicotinic acetylcholine receptor (nAChR) subunits was investigated in the cryostat sections of mouse diaphragm muscles using the indirect immunofluorescence technique. The specific immunolabelings with monoclonal antibodies (mAbs) to beta 2 and to alpha 8 subunits of neuronal nAChR were observed at the endplate determined by labeling with a fluorescent dye (BODIPY)-conjugated alpha-bungarotoxin. The immunoreactivity of mAb to the alpha 3 subunit of neuronal nAChR was detected on the motor nerve fibers including the nerve terminals. These results provide evidence that the subtypes of postsynaptic nAChR, recognized by the anti-beta 2 and/or anti-alpha 8 mAbs, and the presynaptic nAChR recognized by the anti-alpha 3 mAb, are present at the neuromuscular junction, in addition to the classical muscle nAChR.