This is a demonstration of local traumatization of articular cartilage inducing mitoses in parts of a joint other than the site of inquiry. Parts of one of the patellar cartilages of the full-grown rabbit were scored while the other knee was subjected only to arthrotomy. Radioactive thymidine and autoradiographic technique demonstrated that labeled chondrocytes appeared not only around the score in the patella but also scattered in the tibia and femoral condyles. Whether the mechanism of regional mitotic stimulation is a reduction of the concentration of the normal cell specific inhibitors of mitosis, or so-called chalones is not known and requires further investigation.