Apoptotic signalling, particularly in the Fas-Fas ligand (FasL) system, was studied in a mouse osteoblastic cell line, MC3T3-E1. A combination of the cytokines tumour necrosis factor-alpha, interleukin-1beta and interferon-gamma activated the Fas-FasL-dependent cell-death system. The cytokines caused significant enhancement of Fas mRNA and Fas protein, and led to apoptotic cell death. Western blot demonstrated that FasL protein was continuously present in MC3T3-E1 cells, although the cytokines had no effect on the induction of FasL. Exogenous FasL caused a decrease in cell viability and a large increase in apoptotic cell death in cells pre-treated with cytokines, indicating that the Fas-FasL system has the potential to cause apoptosis in osteoblastic cells. Treatment with anti-Fas IgG (antagonistic antibody) inhibited the DNA fragmentation induced by cytokines in a dose-dependent manner, suggesting that cytokine-induced Fas may cause apoptotic cell death in MC3T3-E1 cells. Taken together, these findings show that cytokine-induced apoptotic cell death was mediated by the autocrine or paracrine Fas-FasL system in mouse osteoblastic cells, and suggest that cytokine-induced apoptosis could have an important role in localised bone destruction associated with inflammatory bone diseases such as periodontal disease.