PURPOSE: The purposes of this study were to examine whether meniscal degeneration in human osteoarthritis(OA) was related with the occurrence of apoptosis, the expression of nitrotyrosine and Fas. MATERIALS AND METHODS: Menisci were obtained from OA patients undergoing total knee replacement arthroplasty and from normal subjects who were operated an above knee amputaton. According to histologic degeneration, menisci were graded to normal, grade 1(mild), grade 2(moderate), and grade 3(severe). Apoptotic cells were identified by TUNEL method and electron microscopy. Meniscal sections were analyzed by immunohistochemistry for the presence of nitrotyrosine and Fas expression. RESULTS: The number of apoptotic cells were significantly increased in OA meniscus compared with normal meniscus(p < 0.05). The number of apoptotic cells were increased with tissue degeneration. On electron microscopy, the typical chromatin condensation in the OA meniscus was shown in apoptotic cell. The number of Fas-expressing cells was significantly higher in the OA meniscus(p < 0.05). Nitrotyrosine immuno reactivity was prominent in the degenerative menisci(p < 0.05). Fas and nitrotyrosine expression were increased with degree of tissue degeneration. An increase in number of apoptotic cells was correlated with tissue degeneration but not with age . CONCLUSION: Apoptosis was suggested as one of the causes in the tissue degeneration of the human OA meniscus. The development of apoptosis in the meniscus may be related with Fas and nitrotyrosine expression but not with age.