Freeze fracture analysis was carried out on the density of orthogonal array subunit particles in the plasma membrane of skeletal muscle of six patients with Fukuyama type congenital muscular dystrophy and seven control cases. The group mean density of orthogonal array subunit particles per one orthogonal array was significantly lower in the plasma membrane of Fukuyama patients. The results suggested the possible impairment of orthogonal array function in the plasma membrane of muscle fibers in congenital muscular dystrophy of the Fukuyama type.