The incidence of colorectal cancer — a major cause of mortality in industrialized nations — is lowest in developing countries, where high levels of enterotoxigenic Escherichia coli (ETEC) infection are seen. Whilst it has been thought that there is a link between cancer and ETEC, the mechanisms that underlie this inverse relationship have been poorly understood. In the February 10 Proceedings of the National Academy of Sciences, G. M. Pitari and colleagues at the Thomas Jefferson University, Philadelphia, USA, show that a bacterial heat-stable enterotoxin suppresses colon cancer cell proliferation by a guanylyl cyclase C-mediated (GC-C) signaling cascade (PNAS, DOI:10.1073/pnas.0434905100, February 10, 2003).