The evaluation of composite anterior cruciate ligament prostheses, the union of an inductor of collagen and a synthetic fibre, are described. They were implanted in 10 sheep models for six months. None of the ligaments were broken, and the dynamic radiography was stable during this time. After harvesting them, a histologic study was performed on the intra-osseou and intra-articular portion, and on the synovial tissue. Biocompatibility was excellent. An osseous anchorage was found in 50% of cases and a fibrous ingrowth with well oriented fibres in each case. The results of this study show that the matrix has only partially played its role, because there was no improvement of fibrous ingrowth compared with other studies. However this fact corresponds to results at only 6 months and it is necessary to identify the type of collagen.