Cultured muscle fibers from patients with sporadic inclusion-body myositis (s-IBM), similar to normal control muscle fibers, 1) did not have beta-amyloid precursor protein (betaAPP) immunoreactivity; and 2) became normally innervated, as evidenced by the following features: full cross-striation, continuous contraction, and acetylcholinesterase and acetylcholine receptors accumulated only at neuromuscular junctions. Thus, factors responsible for betaAPP accumulation and denervation-like changes in s-IBM muscle biopsies are not operative in the relatively short-term, non-aged, cultured s-IBM muscle fibers.