Abstract
1. The response of re-innervated muscles to depolarizing blocking drugs was studied.2. During the early stages of re-innervation the ;new' neuromuscular junctions are more sensitive to decamethonium and suxamethonium. The recovery from the block and the repolarization of the end-plate are markedly slowed.3. This increased sensitivity does not appear to be characteristic of all newly formed neuromuscular junctions. It was found that in new-born kittens the muscles are very insensitive to neuromuscular blocking drugs.4. It is concluded that the increased sensitivity of re-innervated muscles to depolarizing blocking drugs and the slow repolarization are due to a persistence of changes which developed during denervation.