Dr. Frampton and his colleagues evaluated the effects of exposing healthy and mildly asthmatic men and women to laboratory-generated ultrafine carbon particles. They hypothesized that ultrafine particle exposure would activate leukocytes and endothelial cells and lead to an inflammatory response in the airway and in the blood; and that it also might affect respiration and cardiac electrophysiologic function. They further hypothesized that effects would be greater in people with asthma than in healthy people. The investigators evaluated markers of airway inflammation in sputum and in blood, and pulmonary and cardiac function before, during and after a 2-hour exposure at rest or with intermittent exercise. They also calculated the number and mass of inhaled particles that deposited in the lungs of the participants.