 Researchers in Italy suggest that highly reactive molecules called reactive oxygen species, ROS, could be recruited as Trojan horses to kill cancer cells, as they are natural regulators of important signalling pathways in cells and can promote programmed cell death. The authors discuss molecular mechanisms underlying the potential anti-cancer activity of various ROS-producing strategies, including drugs and light-stimulated therapies, and expect modifying a production of ROS to have potential for developing new treatments. This article was authored by Bruno Parillo, Masia Di Donato, Antonio Pozzoni, and others.