Adecade-long war over genetically modified mice still rages. In 1994, Klaus Rajewsky's laboratory at the University of Cologne in Germany created the first transgenic conditional knockout mouse.[1] With this mouse, researchers could turn on a genetic mutation at a specific period of development in a specific type of cell. Rajewsky assumed that his mouse would soon be used in labs throughout the world. Simply pleased with his research success, he never considered applying for a patent on a mouse. "It was a European university, and we didn't work that way," he says. Nonetheless, Rajewsky soon found that DuPont of Wilmington, Del., worked just that way.