The intermediate filament protein vimentin, the neonatal isoform of the myosin heavy chain gene (MHCn), and the neural cell adhesion molecule (NCAM) are developmentally and/or neurally regulated molecules that reappear transiently after the induction of necrosis, or denervation. Immunostaining using antibodies against these molecules helps to identify regenerating and/or denervated muscle fibres even if they are not recognized by conventional staining procedures. This study examined the expression of vimentin, MHCn, and NCAM using immunohistochemistry in 82 biopsy specimens from muscular dystrophies, inflammatory myopathies, and neurogenic atrophies. Anti-vimentin labelled significantly more fibres than anti-MHCn staining in the inflammatory myopathies (P<0.03) but not in the muscular dystrophies (P=0.58) and neurogenic atrophies (P=0. 58). The fraction of NCAM+ fibres was always more elevated than vimentin+ or MHCn+ fibres. In the necrotizing myopathies, most NCAM+ fibres were regenerating ones (co-expressing vimentin). In neurogenic atrophies, half the NCAM+ fibres were regenerating and half of them were NCAM+/vimentin- and thus were considered to be denervated. Taken together, anti-vimentin staining detects a broader spectrum of regenerating fibres than anti-MHCn, at least in the inflammatory myopathies. The number of anti-NCAM labelled fibres in the necrotizing myopathies is similar, but not identical, to the number of regenerating fibres. Co-staining with anti-vimentin (or anti-MHCn) and anti-NCAM identifies a subset of fibres that is considered to be denervated.