Hundreds of millions of people around the world are exposed to potentially dangerous levels of arsenic in their drinking water. Arsenic is associated with multiple forms of cancer, especially cancer of the lungs and bladder. The pathogenic mechanism of arsenic is thought to cause damage through the promotion of inflammation and oxidative stress. Obesity is also associated with increased inflammation and oxidative stress, and has been linked to an increased incidence in bladder cancer of arsenic-exposed individuals. We will investigate a potential interaction between arsenic and obesity on lung function in arsenic-exposed adults in northern Chile.