The motor end-plate fine structure and distribution of junctional acetylcholine receptors (AChRs) in patients with amyotrophic lateral sclerosis (ALS) were studied. Morphometric analysis was carried out in 74 end-plates (92 innervated and 47 denuded postsynaptic regions) from 10 patients with ALS. AChR was studied by means of peroxidase-labeled alpha-bungarotoxin binding in 45 end-plates (86 innervated and 36 denuded postsynaptic regions) from 6 patients with ALS. The postsynaptic regions were denuded of their nerve terminals in 33.8% (9.8% in controls). However, the postsynaptic folds in denuded regions were fairly well preserved, as were junctional AChRs. No highly simplified postsynaptic regions were observed. These results suggest that reinnervation of the skeletal muscle by nerve sprouting in ALS may occur in the previously denuded postsynaptic regions and the preserved postsynaptic regions including AChRs, the basement membrane, and Schwann cells may play an important role in this process.