SUMMARY1. A histological and electrophysiological study has been made of the formation of synapses in soleus and extensor digitorum longus muscles of adult rats regenerating from minced muscle fragments.2. In the first 8 days of regeneration, myoblast and myotubes formed within the basement membranes of degenerating myofibres.3. Eleven-to fourteen-day regenerates contained fasicles of myotubes and myofibres and both nerves and spontaneous miniature end-plate potentials (m.e.p.p.s) were observed for the first time, although very few synapses show evoked end-plate potentials (e.p.p.s).4. Eighteen-to twenty-six-day regenerates contained myofibres on which only a single end-plate could be detected; 30 % of these synapses had a normal amplitude-frequency distribution of m.e