Kawai et al. (1990) showed that the extensive regenerative changes in glycerol-induced experimental myopathy, which we observed at 7–14 days after glycerol injection, are similar to those seen in muscles from patients with Duchenne muscular dystrophy. In the present study, using morphologic examination, we also found that As2O3 (0.5 and 5 ppm) effectively suppressed myogenin expression and retarded muscle regeneration in mouse soleus muscles after injury by glycerol. These results suggest that As2O3 is capable of inhibiting skeletal muscle differentiation and retarding muscle regeneration. The gene discussed is MYOG; the disease is myopathy.