The effect of indoor and outdoor paniculate level on respiratory health was examined in 1,576 never smokers, 40 to 69 yr of age residing in industrial, residential, and suburban areas. The health outcomes of interest in this report were physician-diagnosed bronchitis, asthma, and six respiratory symptoms including chronic cough, chronic phlegm, bouts of cough and phlegm, shortness of breath (SOB), wheeze, and wheeze with SOB. Households with coal stoves had substantially higher indoor particulate levels than those with gas stoves. Subjects were grouped into three exposure categories according to the indoor use of coal stoves for both cooking and heating (B), either cooking or heating (E), or neither (N). The adjusted odds ratios for chronic phlegm, bouts of cough and phlegm, wheeze, and wheeze with SOB were significantly higher in the B than in the N group; the odds ratios for chronic cough and SOB were also higher for B than N, although these were not significant. The odds ratios in the E group were significantly greater for wheeze with SOB than in the N group but not for the other symptoms. The global estimates of the odds ratios for the six symptoms were 1.4 and 2.0, respectively, for the E and B groups. The particulate level was highest in the industrial area and lowest in the suburban area. There was an excess risk of all respiratory symptoms among subjects residing in industrial and residential areas, with an increase in symptom prevalence with outdoor particulate levels. The estimated global odds ratio was 2.5 (95% confidence interval [CI]: 1.3 to 4.8) for a unit (natural logarithm μg/m3) increase in particulate level. The association become undetectable when indoor coal combustion was removed from the regression model. The total particulate exposure, represented by the sum of indoor and outdoor particulate exposure scores, was significantly associated with increased prevalence of all the six symptoms. A similar trend was noted for bronchitis. However, particulate level showed no association with physician-diagnosed asthma. This study suggests that both indoor and outdoor particulate exposure may be important risk factors in the development of chronic obstructive pulmonary disease. Indoor air pollution could confound the effects of outdoor air pollution if not simultaneously taken into account.