This study suggests that the thermal burden of poorly ventilated parked automobiles can be considerable, particularly when the automobiles are exposed to direct sunlight. Leaving the windows open two inches does not appear to be protective. The practice of exposing infants and toddlers to such thermal risk appears to be common and the need for adequate ventilation unrecognized. Education measures stressing the use of carseats and other safety devices should include the potential hazards of high temperature in parked automobiles.