Female athletes tear their anterior cruciate ligaments (ACLs) more frequently than male athletes participating in similar athletic events do. The reasons for this discrepancy are not known. Many possible causative factors, such as size, strength, anatomic, social, and hormonal differences, have been suggested. The possible involvement of normal tissue remodeling events in susceptibility to ACL injury has not been thoroughly examined. We are characterizing gender differences in matrix metalloproteinases and their inhibitors. Results of these studies are summarized and discussed in the context of tissue remodeling in general, with an emphasis on the cell biology of ACL repair.