There have been few reports regarding the metabolic effects of X-ray irradiation on adult human articular chondrocytes. The purpose of this study was to evaluate whether exposure to X-ray irradiation during tumor surgery can cause impaired metabolism in adult articular cartilage. To achieve this we exposed cultured chondrocytes isolated from normal or degenerated cartilage to varying doses of Xray irradiation, then measured apoptosis, and the production of chondroitin sulfates (CS), prostaglandin E2 (PGE2) and p38 mitogen-activated protein kinase (MAPK) in these cells. The number of apoptotic cells was not affected by irradiation in chondrocytes from normal or degenerated cartilage. Likewise, the production of C6S and C4S was not altered by irradiation in either group. The concentration of PGE2 in non-degenerated chondrocyte cultures did not change with radiation in a dose-dependent manner. However, the concentration of PGE2 in degenerated chondrocytes increased in a radiation dose-dependent manner. Irradiation at 10 Gy, in degenerated chondrocytes, induced remarkable activation of p38. This suggests that it is important to consider whether there is an osteoarthritic joint in the area that is to receive radiation therapy during tumor surgery.