1. Tritiated thymidine autocardiography was used to study the response of articular cartilage to three types of surgically cleated wounds in the distal part of thirty-five femora of immature rabbits. The response of time cartilage was identical in each type of trauma.
2. The cartilage responded within twenty-four hours by marginal necrosis which extended four to six cells from the defect. This disappeared by three weeks in most of the animals studied.
3. An intense proliferative activity began on the first day arid extended eight to twelve cell widths from the necrotic zone on either side of the wound. This response diminished and could no longer be observed histologically or autoradiographically by two weeks. There was no evidence in the six weeks of this study that this proliferation contributed materially to wound healing.
4. Articular cartilage appears to respond to trauma in a manner identical with the response of most other body tissues, with one major exception: it undergoes necrosis and proliferation but lacks the vascular response of inflammation.