AbstractChanges of cytoskeletal architecture and incorporation of3H‐proline were investigated in contracted anterior cruciate ligaments with use of a model of contracture. In control ligaments, fibroblasts were shown by immunofluorescence microscopy to contain actin, vimentin, and myosin in their cytoplasm. Cytoskeletons were visualized by electron microscopy as a mesh network of microfilaments among cell organelles. In contracted anterior cruciate ligaments, fibroblasts were spindle‐shaped and their cytoplasm could not be observed clearly in sections stained with hematoxylin and eosin. Actin staining was distributed irregularly and extensively, whereas vimentin and myosin staining was not scattered so extensively. When compared electromyographically, the actin staining appeared in cytoplasmic pseudopods of the fibroblasts. It was thought that these cytoplasmic pseudopods contained mainly actin and little or no other cytoskeletal elements such as vimentin and myosin. In autoradiographs, contracted anterior cruciate ligaments were shown, with use of3H‐proline, to experience a decrease in the number of labeled cells. On the basis of these findings of cytoskeletal rearrangement and of decreased incorporation of3H‐proline, we hypothesized that fibroblasts of the anterior cruciate ligament had the capacity to change their character during knee immobilization and to play a role in ligament cont