We compared functional and structural recovery from imposed muscle injury in mdx and wild type mice to test their regenerative capacity. Soleus muscle, known to be particularly affected by the disease process, was subjected to most severe damage caused by freeze injury plus 'bystander damage'; the latter causes destruction of host muscle cells in the course of immune rejection of implanted non-histocompatible myogenic cells. Freezing/implantation was performed in mdx and control mice at two ages (4-6 months, "young' and 10-12 months, 'old' age). While recovery of muscle force in the control groups reached 77 and 88% of contralateral by 3 and 6 months, it was 60% and only 43% in mdx mice damaged at young and old age, respectively. Larger force deficits in mdx mice were due to loss of muscle tissue as measured from desmin-positive areas. Worse recovery of dystrophic muscles in general, and old muscles in particular, is interpreted to indicate pronounced exhaustion of the regenerative capacity, possibly caused by previous cycles of degeneration and regeneration.