Prodded by environmental activists, politicians, and the media, the European Patent Office (EPO) has said that it made a mistake last December in granting too broad a patent on a method to isolate genetically engineered stem cells. Last week EPO officials declared that the patent should have been restricted to "nonhuman" animals to prevent the possible cloning of humans. The German government has announced its intention to file a formal complaint, and the company licensed to use the technology says it is eager to work with EPO officials "to rectify the problem."