In order to investigate the effects of reduced and subsequently increased neuromuscular activity on muscle acetylcholinesterase (AChE), rats had one hindlimb immobilized with plaster casts for 4 weeks and were killed either at the end of immobilization (group I), after 4 weeks of resumed normal activity following cast removal (group R), or after 4 weeks of resumed activity supplemented with a daily treadmill-walking task (group E). Immobilization resulted in a decrease in adductor longus muscle weight to 66.4% of control; total muscle end-plate-associated AChE was decreased to 51.4%. Total muscle ACh hydrolysis was not significantly affected. Mild daily exercise during recovery increased total muscle end-plate AChE to control levels after 4 weeks, while in group R the corresponding level was significantly lower (84.4%). Decreased neuromuscular activity has different effects on end-plate AChE and non-end-plate AChE. Mild endurance-type overload during recovery from immobilization can accelerate recovery of end-plate AChE activity to normal.