Twenty-four implantations of heterologous connective tissue structures replacing ligaments and tendons are evaluated in order to present the early results in the heterologous replacement of cruciate ligament structures. Twenty implantations are analysed after 18 to 36 months. The biologic structure which is very strong in comparison with the autologous tissue is not modified to a great extent during a period of 21 months, i.e. the ligament prosthesis remains unchanged so that the appellation "bio-prosthesis" seems justified. At present the preliminary clinical results are satisfying. Consequently, heterologous connective tissue structures can be used in repeated surgical interventions for the stabilization of chronic ligament instabilities.