Objectives: Clinical experience indicates that shorter duration of denervation is associated with better recovery of muscle function. FK506 (Tacrolymus), which is in clinical use as an immunosuppressant drug, has been demonstrated to increase the rate of nerve regeneration in a dose dependent fashion. We hypothesize that FK506 can expedite the recovery of muscle mass and maximal force capacity in the rat EDL muscle following peroneal nerve transection and repair. Methods: Peroneal nerve was transected and repaired on the left and no surgery was done on the right hindlimbs of 9-month-old male F344 rats. The rats were then randomly assigned to either FK506 group (n=8) or CONTROL group (n=8). FK506 group was treated with daily injections of FK506 (1 mg/kg), and CONTROL group with daily injections of vehicle solution. Injections were administered subcutaneously at 5 days/week for 3 weeks. An injection-free week preceded evaluation. Four weeks postoperatively, bilateral measurements for maximal force capacity and mass of EDL muscles were made. Results: For denervated-reinnervated muscle, there was no difference of maximum force capacity (CONTROL=555±47 mN, FK506=536±35 mN; p=.750) and muscle mass (CONTROL=67±4 mg, FK506=75±2 mg; p=.068) at 4-week-recovery as a result of FK506 administration. For nerve- intact muscle, there was no difference of maximum force capacity (CONTROL=3628±18 mN, FK506=3697±168 mN; p=.783) and muscle mass (CONTROL=148±5 mg, FK506=144±5 mg; p=.537) at 4-week-recovery as a result of FK506 administration. FK506 treated animals experienced more weight loss than CONTROL rats following nerve repair surgery. Conclusions: FK506 did not expedite force recovery of denervated-reinnervated muscle in this model. FK506 had no detrimental effect on nerve intact muscle force.