The purpose of this study was to determine if a ligament-muscle reflex arc exists between the bone-patellar tendon-bone autograft after anterior cruciate ligament (ACL) reconstruction and the hamstring muscle group. We studied four patients, average age 34.2 years (range 32-36 years). The mean time between the ACL reconstruction and the study examination was 56.2 months (range 5-108 months). All patients underwent a second-look arthroscopy for meniscal injuries, cyclops lesions, or adhesions. Five patients with a normal ACL served as a control group before we performed an arthroscopic meniscectomy. Electromyographic (EMG) activity was measured using fine wire electrodes under two different testing conditions. No unequivocal EMG activity could be detected in the ACL-reconstructed knees when we pulled on the graft or in the controls. Three of four patients and all controls felt pain when we touched the graft or normal ACL or applied strain on it with the hook. In conclusion, the ACL autograft presents a noxious sensory innervation, the Lachman test maneuver stimulates a reflex arc with hamstrings activation, and an unequivocal ligament-muscle reflex arc from the graft to the hamstring muscle group could not be demonstrated.