With suitable radioactively labelled precursors the mitotic (using 3H-thymidine) and the productive metabolisms (using 3H-proline and 35S-sulphate) were investigated on various kinds of joint- etc. cartilage from mice with genetically caused arthrosis. The autoradiographic analyses were performed using 3H-thymidine-, 3H-proline- and 35S-sulphate-indices and the statistical evaluation of the findings led to the following results: the synthesis level of sulphated glycosaminoglycans (GAG) in the cartilage ground substance is lower for 5--6 month-old mice than for the 16--17 month-old animals of this genetic arthrosis strain. This is most distinct in the 3rd (= basal) zone of the knee-joint cartilage which increased to double the comparable value in this period. In all 3 zones of the knee-joint cartilage GAG-synthesis is considerably greater than the collagen synthesis according to these autoradiographic analyses. These findings can be detected before any histologically or histochemically demonstrable cartilage alterations and represent therefore the earliest signs of a so-called "pre-arthrosis". Collagen synthesis decreases thereby, and the same holds for DNA-synthesis and the mitotic metabolism of the cartilage cells - according to the findings to date. However the question is still under investigation whether arthrosis (like atherosclerosis) also starts with an increase in cell-turnover. This question is not only of theoretical interest, it has practical clinical consequences, even for the treatment. These investigations also serve this clinically relevant question because arthrosis is the most common human joint disease.