Genetically modified maize causes cancer: that was the gist of one of the most controversial studies in recent memory, published in September 2012 by Food and Chemical Toxicology. [But] on November 28th the journal retracted it. The article was by Gilles-Eric Sralini of the University of Caen, in France, and his colleagues. It described what happened to rats fed with NK603 maize, a variety made resistant to a herbicide called glyphosate by a genetic modification made by Monsanto. Monsanto also discovered glyphosate's herbicidal properties. It sells it under the trade name Roundup". In Dr Sralini's experiment, rats fed with the modified maize were reckoned more likely to develop tumours than those which had not been. Females were especially badly affected: their death rates were two or three times as high as those of control groups. The article was explosive. Jean-Marc Ayrault, France's prime minister, said that if its results were confirmed his government would press for a Europe-wide ban on NK603 maize. Russia suspended imports of the crop. Kenya banned all GM crops. Though the paper has been retracted, that is unlikely to be end of the matter. The journal's publisher said there was "no evidence of fraud or intentional misrepresentation of the data", which are the usual justifications for retraction. Scientific opinion runs strongly against the conclusion that GM foods are harmful-but not universally so. A group called the European Network of Scientists for Social and Environmental Responsibility backed Dr Sralini.