Skeletal muscle satellite cells were isolated from soleus and extensor digitorum longus muscles of Sprague-Dawley rats at selected ages between 6 days and 30 months and grown in cell culture. Cells at each donor age were monitored individually to determine the number of progeny they were capable of producing. Under identical in vitro conditions, the average number of progeny produced was inversely proportional to donor age. Hence, the proliferation potential of satellite cells decreases with age.