Researchers said they have found a cancer-causing chemical in the bodies of people exposed to secondhand smoke, a discovery that could increase understanding of how passive smoking can cause cancer. The compound, NNK, is found in the urine of people exposed to tobacco smoke, but was not found in those who had not been exposed to secondhand smoke, Stephen Hecht and colleagues at the University of Minnesota Cancer Center in Minneapolis found. "This is the first time that a metabolite of a tobacco-specific lung carcinogen has been found in the urine of nonsmokers exposed to environmental tobacco smoke under field conditions," Hecht said in a statement released at a Las Vegas meeting of the American Chemical Society, where the findings were presented. His team collected urine samples from nine hospital workers who were caring for smoking patients in a Canadian veterans hospital. All the workers had signs of NNK in their urine, although at levels 70 times lower than those found in smokers. NNK has been found to cause adenocarcinoma in animal studies. Tobacco companies have maintained that there is no evidence secondhand smoke causes illness.