The objective of this study was to determine whether genetic polymorphisms in enzymes that metabolise oxidative agents modify the individual susceptibility to developing asbestos and smoking-related pleuropulmonary changes. Nine polymorphisms of six genes (EPHX1, GSTM1, GSTM3, GSTP1, GSTT1 and NAT2) were genotyped from 1,008 Finnish asbestos-exposed workers. The genotype data were compared to signs of lung fibrosis and pleural thickenings, as well as with total lung capacity, single-breath diffusing capacity of the lung for carbon monoxide (D(L,CO)) and specific diffusing capacity (expressed as D(L,CO) per unit of alveolar volume (V(A))). The GSTT1 deletion polymorphism was associated with fibrotic changes (p=0.003), and decreased D(L,CO) (p=0.02) and D(L,CO)/V(A) (p=0.002), and the GSTM1 deletion polymorphism was associated with the greatest thickness of pleural plaques (p=0.009). On further analysis, the GSTT1 null genotype was found to pose over a three-fold risk for severe fibrotic changes (OR 3.12, 95% CI 1.51-6.43), and around two-fold risks for decreased D(L,CO) (OR 1.77, 95% CI 1.06-2.95) and D(L,CO)/V(A) (OR 2.37, 95% CI 1.33-4.23). In addition, the GSTM1 null genotype showed an elevated risk (OR 1.36, 95% CI 1.03-1.80) for thicker pleural plaques. Our data suggest that inherited detoxification capacity may affect the development and severity of asbestos and smoking-related nonmalignant pulmonary changes.