Cultured muscle cells from Duchenne muscular dystrophy (DMD) patients show altered growth from the mononucleated stage: abnormal morphology, decreased adhesiveness, reduced number of population doublings and delayed fusion. On the basis of these findings, a study was undertaken to observe cell shape and surface morphology by scanning electron microscopy and to define the immunocytochemical localization of 4 basal lamina components (type IV collagen, laminin, fibronectin, heparan sulfate proteoglycan (HSPG]. Eight DMD muscle cultures with fusion indices higher than 65% were compared to muscle cultures from 10 age-matched controls. The following results were noted for the dystrophic muscle cells: (1) the cell surface was smooth with a few slender cell processes and anchorage extensions; (2) distribution of type IV collagen and laminin was heterogenous, with large patches (type IV collagen) or a reticulum (laminin); (3) in contrast, fibronectin and HSPG levels were clearly decreased. These molecules did not form a network but rather were arranged in thick filaments and patches. Cell surface morphology may be related to the decreases in fibronectin and HSPG, which could reflect a more general decrease in basal lamina. Such findings could explain the low adhesiveness of the cells from dystrophic cultures and the delayed fusion of myoblasts. Although these abnormalities were maximally expressed after myoblast fusion, they were already present in mononucleated cells and their connection with the primary defect in DMD, i.e., lack of dystrophin, must now be clarified.