Introduction: Exposure to particulate matter (PM) may induce inflammation and oxidative stress in the airways. Carriers of null polymorphisms of Glutathione S-Transferases (GSTs), which detoxify reactive oxygen species, may be particularly susceptible to the effects of PM. Objectives: to investigate whether deletions of GSTM1 and GSTT1 modify the potential effects of exposure to indoor sources of PM on symptoms and objective markers of respiratory disease. Methods: We conducted a population-based cross-sectional study of 3,471 persons aged 18-69 years. Information about exposure to indoor sources of PM and respiratory symptoms was obtained by a self-administered questionnaire. In addition, measurements of lung function (spirometry) and FeNO were performed. Copy number variation of GSTM1 and GSTT1 was determined by PCR-based assays. Results: We found that none of the symptoms and objective markers of respiratory disease were significantly associated with the GST null polymorphisms. An increasing number of positive alleles of the GSTM1 polymorphism tended to be associated lower prevalence of wheeze, cough, and high FEV(1) , but these trends were not statistically significant. Furthermore, we did not observe any statistically significant interactions between GST copy number variation and exposure to indoor sources of PM in relation to respiratory symptoms and markers. Conclusions: In this adult population, GST copy number variations were not significantly associated with respiratory outcomes and did not modify the effects of self-reported exposure to indoor sources of PM on respiratory outcomes.