Twenty-six anterior tibial muscle specimens were analyzed with the electron microscope 2 h, 1, 4, 18, 45, 90 and 226 days after temporary ischaemia of the rat hind leg produced by pneumatic tourniquet for 1, 2, 3, 4 and 6 h. No ultrastructural alterations were seen after 1 h ischaemia, but reversible disappearance of muscle glycogen and swelling of muscle and nerve mitochondria occurred after 2 h ischaemia. Irreversible alterations such as disappearance of the Z-line, disruption of cell membrane and vacuolation of muscle mitochondria were observed after ischaemia of 3 h and longer in a part of the muscle fibres. Ischaemia for 6 h was followed by autolysis of all the muscle fibres within the specimens. Autolysis and phagocytosis of the remnants of the affected fibres was present on the 4th day. On that day regenerative phenomena were also observed, such as satellite cells and young myotubes. The fine structure of the muscle fibres was normal on the 18th day after the temporary ishcaemia, although some size variation of the muscle fibres was still observed. Degeneration of a part of the presynaptic nerve endings of motor end-plates with or without simultaneous degeneration of the postsynaptic muscle fibre was seen after ischaemia lasting 3 h or longer. Motor end-plates were first seen on the 45th day in the muscle subjected to 6 h ischaemia and were most likely regenerated ones.