We studied three new cases of congenital muscular dystrophy (CMD) with homogeneous clinical and laboratory features, represented by congenital muscle hypotonia and weakness, early contractures, elevated serum CK, and dystrophic pattern at muscle biopsy, without clinical impairment of CNS. Merosin, the laminin isoform that contains the alpha 2 heavy chain, was absent in muscle fibers of all the patients by immunohistochemistry and by immunoblot. By electron microscopy, we found a severe disruption of muscle fiber basal lamina, but not of blood vessel basal lamina, which contains the laminin alpha 1 heavy chain isoform. This disruption may play a key role in the degeneration of muscle fibers and in the abnormal proliferation of connective tissue seen in CMD.