This report describes two pilot investigations for a longitudinal study of infants designed to determine if NO2 exposure from cooking stoves increases the incidence or severity of respiratory infections during the first 18 months of life. In the first study, Drs. Samet and Spengler selected 147 households with electric or gas stoves and infants for home indoor monitoring of NO2 concentrations; the infants\' mothers completed a daily calendar-diary on respiratory symptoms and provided illness information every 2 weeks. The second pilot study was designed to refine the system for illness surveillance. Seventy-five infants were followed over a 4-month period during which results from biweekly or weekly surveillance calls were compared with clinical assessments of healthcare providers and viral culture results.