Objective. The purpose of this study was to investigate the effect of interleukin-1 on cells from loose bodies of synovial chondromatosis of the temporomandibular joint. Study design, The cells were isolated from uncalcified loose bodies in a case of synovial chondromatosis of the temporomandibular joint and cultured in alpha-MEM medium containing 10% fetal bovine serum. The cells were treated with or without interleukin-1 alpha and then stained with toluidine blue. Their conditioned media were analyzed with gelatin zymography to detect matrix-degrading proteinase(s). Results. The cells from loose bodies produced toluidine-blue-stained matrix. When the cells were treated with 100 ng/ml of interleukin-1 alpha for 3 days, toluidine-blue-stained matrix was strikingly reduced. Gelatin zymography revealed that interleukin-1 alpha-treated cells released 62-kDa gelatinase. Conclusions. Interleukin-1 alpha may lead loose-body-derived cells to degrade the cartilaginous matrix of loose bodies in synovial chondromatosis of the temporomandibular joint.