Ever since Lexer's first attempts to remedy destroyed knee-joints by transplanting homioplastic material, the cup joint transplantation as developed by Pap and Krompecher has proved to be expedient and suitable thanks to the recent work performed by Wolkow. In order to assure that the process is safe from the mechanical standpoint, i.e. guarantee an accurate fit of the transplant to the recipient joint portion, in particular in the femur condyle area, the author has developed a method whereby the joint cups are cut rut of the donor material in accordance with pre-produced patterns and the oecipient joint portion is shaped to the correct form by means of similar patterns produced on the basis of X-rays.