We investigated the effect of IFN gamma or IFN gamma/IFN alpha and IFN gamma/TNF treatment on the apoptosis of Ewing tumor cells (SK-N-MC). The results show that treatment of cells with IFN gamma resulted in 17% of cell death while no effect was observed when cells were treated with IFN alpha or TNF alone. Percentage cell death increased markedly in IFN gamma/IFN alpha- and IFN gamma/TNF-treated cells (42% and 67%, respectively) as compared to IFN gamma-treated cells. These results suggest that IFN alpha and TNF amplified the apoptotic signal(s) induced by IFN gamma. It was shown recently that Ewing cells undergo apoptosis upon treatment with recombinant TRAIL (TNF-related apoptosis inducing ligand), a member of the TNF family. Thus, since cytokines were reported to be able to induce TRAIL in other cell systems, we were prompted to investigate whether TRAIL induction was involved in the mechanism responsible for IFN gamma-mediated cell death in Ewing cells. The results reported here are consistent with the notion that cell-associated and secreted TRAIL contribute in an autocrine or paracrine manner to the triggering of Ewing cell apoptosis induced by IFN gamma alone or combined with IFN alpha or TNF. The observations reported here might contribute to the development of alternative new approaches to the treatment of Ewing tumors resistant to conventional therapy.