Characterization with a panel of six antibodies revealed abnormal dystrophin expression in 6 of 20 Duchenne muscular dystrophy (DMD) carriers examined, and in 5 of 12 Becker muscular dystrophy (BMD) carriers examined. The immunocytochemistry of muscle fibres was normal with five of the antibodies in two BMD carriers, but some muscle fibres were negative to the antibody directed against a portion of the dystrophin rod domain. Mosaicism was detected with all six antibodies in the other three BMD (but in only a small number of fibres) and in all DMD carriers muscles. Spectrin, vinculin and talin were immunolocalized in the same muscle specimens in order to assess membrane cytoskeletal integrity and to correlate their expression with that of dystrophin. These proteins, including vinculin, which was previously reported to be reduced in DMD patient muscles, were normally present on the surface of all dystrophin-deficient fibres. Muscle fibre types were characterized using monoclonal antibodies against fetal myosin and adult fast and adult slow myosin heavy chains. In both the DMD and BMD carriers, a significant reduction in type 2B fibres, as well as an increase in type 2C and fetal myosin-containing fibres was found - as has also been reported in DMD patients. Altered dystrophin expression was observed more frequently in type 2 than type 1 fibres. Dystrophin deficiency was found in a high percentage of type 2C fibres as well as in all fibres expressing fetal myosin; this suggests that dystrophin-deficient fibres are more susceptible to degeneration, leading to regeneration.