Animal and controlled human studies indicate that exposure to acidic aerosol affect airway reactivity, mucociliary clearance and pulmonary airflow. Preliminary data suggests that long term exposure to low level ambient acidic aerosol may be associated with chronic lung disease, particularly bronchitis. The U.S. EPA is actively considering an Ambient Air Quality Standard for acidic aerosol. Such a standard would initiate a major national regulatory control effort based on a few, methodologically weak, studies. Epidemiologic studies of an association between acidic aerosol and health effects have been handicapped by the pronounced spatial and temporal variability of ambient acidic aerosol, the low outdoor concentrations, presence of confounding air contaminants and difficulties assessing exposures. It has been assumed that residential indoor exposures do not exist and not studies of indoor exposures have been done. We have identified unvented kerosene space heaters as a major source of indoor acidic aerosol. These results are confirmed in field measurements. Given the potential for the number of individuals exposed (18 million heaters have been sold in the U.S. and they are a major source of home heat in a number of countries) and the levels of exposure, kerosene heater users would constitute a unique population in which to determine the nature of an association between acidic aerosol exposure and respiratory health effects. This study tests the hypothesis that exposures to elevated concentrations of acidic and sulfate aerosol air contaminants, resulting from kerosene heater use are associated with an increased risk of acute or chronic upper and lower respiratory symptoms in infants age 6-24 months (a sensitive population), including cough, phlegm, wheeze, runny/stuffy nose, etc. The hypothesis that the nonsmoking exposed mothers of the infants are also at an increased risk of respiratory symptoms and reversible decrements in peak expiratory flow is also tested. these associations will be evaluated for a dose response relation while adjusting for other known risk factors (environmental tobacco smoke, NO2, maternal smoking, health status, etc.). The study population will be selected from 8,700 live deliveries occurring at YHN Hospital during a 18 month period. The exposed infants (N=300) and their nonsmoking mothers (N=228) will live in homes using kerosene heaters. They will be compared to a control group of infants (N=600) and their nonsmoking mothers (N=456) not using kerosene during the nono-heating season including reports of respiratory symptoms in both the infants and mothers and concurrent use of the heater. Diurnal peak flow differences for the mothers for a two week period during the heating and non-heating season will be recorded. A nested-exposure assessment protocol will be employed and potential confounding factors will be controlled. If seasonal differences are found for symptom rates and pulmonary function measurements this design will allow for a distinction between exposure effects and seasonal variation effects. This study will have important implications in determining whether an Ambient Air Quality Standard is needed for acidic aerosol to protect the public health. It will also identify any increased health risk for the large population of kerosene heater users.