Exposure to indoor combustion has been associated with health effects, especially in women, in many parts of the world. The authors studied 648 nonsmoking women in nonsmoking households who measured their peak expiratory flow rate for 2 weeks, during the winter, when ambient air pollution is lower. The participants recorded any use of secondary home heating combustion sources (eg, kerosene heaters, fireplaces, wood-burning stoves). Peak expiratory flows were expressed as the variability percent mean for the 2-week measurement period. Adjusting for educational level, ethnicity, and history of allergies, the 2-week variability in peak expiratory flow was associated with a previous physician diagnosis of asthma (OR = 2.88; 95% CI = 1.59-5.21) and black or Hispanic ethnicity (OR = 2.02; 95% CI = 1.27-3.22), but was not associated with use of any supplementary home combustion sources among either asthmatic or nonasthmatic women.