Ewing's sarcoma family of tumours (ESFT) are childhood cancers whose aggressive behaviour and propensity to relapse prompts the need for new treatment approaches. In this study, the role of cellular antioxidants in determining the sensitivity of ESFT cell lines to the cytotoxicity of the antineoplasic agent fenretinide was investigated with a view to identifying targets for the development of new treatment strategies. ESFT cell lines differentially express cellular antioxidants, although cellular glutathione (GSH) was identified as the major determinant of sensitivity to fenretinide. The importance of GSH in ESFT physiology was demonstrated by the depletion of intracellular GSH using l-buthionine (S,R) sulphoximine (BSO), which decreased cell viability. Furthermore, pre-treatment of ESFT cells with BSO sensitised them to fenretinide-induced death. Overall, these results demonstrate that ESFT cells are sensitive to changes in intracellular redox environment, and that targeting specific cellular antioxidants might be a viable strategy in treating ESFT.