The fate of mechanoreceptors was studied in torn and reconstructed anterior cruciate ligaments in animals and in humans. In untreated anterior cruciate ligament lesions in humans, morphologically normal mechanoreceptors remained in the ligament for 3 months after the injury. After that time, their number gradually decreased. By the 9th postinjury month, only a few free nerve endings were present. Even free nerve endings were totally absent in the biopsy specimens from 1-year-old lesions. In experimental animals, anterior cruciate ligament reconstruction with autologous patellar tendon resulted in the presence of mechanoreceptors in the reconstructed anterior cruciate ligament. When an artificial ligament was used, no mechanoreceptors were found. Morphologically normal mechanoreceptors were present in 2 patients with a lax biologic anterior cruciate ligament reconstruction 9 and 10 years after the operation.