The storm of scientific criticism over claims that a genetically modified (GM) maize causes severe disease in rats shows no signs of abating. Gilles-Eric Séralini, a molecular biologist at the University of Caen, France, is under intense pressure to report the full data behind his team’s finding that rats fed for two years with Monsanto’s glyphosate-resistant NK603 maize (corn) developed many more tumours and died earlier than controls (see Nature 489, 484; 2012).