Motor nerve terminals of fast muscles (lateral head of gastrocnemius, l. g. medial head of gastrocnemius, m. g.) and slow muscles (soleus, sol.) in 4 healthy adult cats were studied in teased muscle fibres with zinc iodide-osmium tetroxide (ZIO) staining. The motor nerve terminals stained with ZIO had a more delicate appearnance than those stained with other methods. It was obvious that fairly marked differences between the strutures of fast and slow muscle end-plate in cat. The terminal sprouts were also different between fast and slow muscle motor nerve terminals. in cat. The percentages of preterminal sprout were mean％?S.D. 8.5?5.4, 7.1?3.2 and 0.3?0.5 in l. g., m. g, and sol. respectively, and the percentages of ultraterminal sprout were 0, 0.3?0.5 and 5.7?2.0 in l. g., m. g. and sol. respectively. In each l. g., m. g. or sol. muscle, not only the size and complexity of end-plates were different, but also there were various kinds of end-plates. All of these showed the different stages of growth, sprouting, degeneration and replacement. The turnover of motor nerve terminal and the factors which influence the morphology of the end-plates in normal adult cat are discussed.