AbstractWe report immunofluorescence observations on normal and dystrophic human muscle using an antibody (anti‐bF) raised against bovine fetal myosin and specific for fetal myosin heavy chains. In rat skeletal muscle, anti‐bF was previously found to react selectively with myosin isoforms expressed during fetal and early postnatal development and in regenerating muscles.11Anti‐bF stained most fibers in human fetal and neonatal muscle, whereas only nuclear chain fibers of muscle spindles were labeled in normal adult muscle. In muscle biopsies from patients with Duchenne's muscular dystrophy, numerous extrafusal fibers were stained: some were small regenerating fibers, others were larger fibers presumably resulting from previous regenerative events. Fetal myosin immunoreactivity in Duchenne's dystrophy appears to reflect the reexpression of fetal‐specific myosin isoforms and provides a new valuable tool for identifying regenerating fibers and following their destiny in dystrophic