Recent studies have demonstrated that the expression of heat shock protein (HSP) was enhanced under stress in joint diseases, such as rheumatoid arthritis and osteoarthritis. The purpose of this study was to analyze the expression of 70Kd HSP in patients with internal derangement of the temporomandibular joint (TMJ) by immunohistochemical and enzyme-linked immunosorbent assay (ELISA) methods. For immunohistochemistry, 5 extirpated discs and 16 synovial biopsy specimens from patients with TMJ internal derangement and 2 extirpated discs from normal subjects were examined. For ELISA, synovial fluid from 11 patients with TMJ internal derangement and from 6 normal volunteers were investigated. The results showed that the 70Kd HSP staining intensity in chondrocytes around the damaged area of the articular discs from patients with TMJ internal derangement was higher than that in chondrocytes in control specimens. In addition, 70Kd HSP expression in synovial fluid from patients with TMJ internal derangement was slightly higher than that in normal subjects. These findings suggest that elevated 70Kd HSP expression is related to the progression of TMJ internal derangement.