1. In 15- to 21-month-old male mice of the C 57 black strain that had been treated with a placebo (olive oil), the incidence of gonarthrosis was found to be 19% in the youngest and 61% in the older animals. If the very early stages are included, the incidences range from 36% to 65%. 2. Only the most severe degrees of arthrosis could be diagnosed radiographically; mild stages were only detectable by histological examination under the light-microscope. 3. The motility of the older animals severely affected with arthrosis (as measured by reference to their ability to run over a grid) was for the most part limited. 4. The percentage of mice with gonarthrosis was diminished by treatment with ethyl-3,5,6-tri-O-benzyl-D-glucofuranoside (tribenoside, Glyvenol) in doses of 150, 500 or 1200 mg/kg p.o. weekly over a period of three months. Comparison of the animals that had received tribenoside with those given the placebo (olive oil) revealed that the incidence of lesions was 36-60% less in the former. If the very early stages of arthrosis were included in the evaluation, the differences were statistically significant (P less than 0.05) at the two higher dose-levels. 5. Under the given experimental conditions, no clear-cut dose-effect relation on the part of tribenoside was demonstrable, since the youngest animals with the least marked arthrosis were treated with the smallest dose of the preparation and the older animals, in which the incidence of arthrosis was higher, with the larger doses.