The pet food contaminant responsible for the deaths of dozens of dogs and cats earlier this year, leading to a major pet food recall, appears to be a combination of two chemicals, melamine and cyanuric acid, according to a new study. Last spring, melamine, a chemical used in plastics and fertilizers, was detected in wheat gluten imported from China that was used as a pet food additive. It was originally suspected as the toxic ingredient in the pet scare, but studies failed to show that it directly caused the deaths. Birgit Puschner and colleagues at the University of California, Davis, now find that cyanuric acid—another contaminant in the food—in combination with melamine causes kidney failure and death in cats (J. Vet. Diagn. Invest. 2007, 19, 616). Cyanuric acid is used in swimming pools and hot tubs to slow the breakdown of chlorine-based disinfectant chemicals. The researchers hypothesize that melamine and cyanuric acid react to form insoluble crystals in the animals' kidneys.