In December 2005, Nature published a news story comparing the accuracy of science articles taken from the website of Encyclopedia Britannica and Wikipedia, an online encyclopaedia that can be edited by anyone. The results and their interpretation have since been disputed by Encyclopedia Britannica. We present our initial formal response to Britannica's objections, an Editorial from the 30 March 2006 edition of Nature, and a point-by-point rebuttal of Britannica's main objections.