The effects of long-term exposure to hyperthermia were studied on several cell cultures of cartilaginous or bone origin after a 4-day treatment at 40 degrees C. Chondrocytes proliferation, as well as mitochondrial activity were not modified by these culture conditions (40 degrees C) but protein content and cell volume were increased. In contrast, the proliferative capacity of osteoblasts, MC3T3.E1 a and ROS 17/2.8 was decreased and their protein content, cell volume and mitochondrial activity were increased. Chondrocytes appeared to be thermoresistant, and osteoblastic cells thermosensitive. Furthermore, temperature sensitivity was greater for the continuous established osteoblastic cell line MC3T3.E1 and for the cancerous established osteoblastic cell line ROS 17/2.8 than for chondrocytes.