The associations between lung cancer risk, mutagen sensitivity (a marker of cancer susceptibility), and a putative lung carcinogen, wood dust, were assessed in a hospital-based case-control study. There were 113 African -American and 67 Mexican-American cases with newly diagnosed, previously untreated lung cancer and 270 controls, frequency-matched on age, ethnicity, and sex. Mutagen sensitivity ( 1 chromatid break/cell after short-term bleomycin treatment) was associated with statistically significant elevated risk for lung cancer [odds ration (OR) = 4.3; 95% confidence intervals (CI) = 2.3-7.9]. Wood dust exposure was also a significant predictor of risk (overall OR = 3.5; CI = 1.4-8.6) after controlling for smoking and mutagen sensitivity. When stratified by ethnicity, wood dust exposure was s significant risk factor for African-Americans (OR = 5.5; CI = 1.6-18.9) but not for Mexican-Americans (OR = 2.0; CI = 0.5-8.1). The ORs were 3.8 and 4.8 for non-small cell lung cancer in Mexican-Americans (CI = 1.2-18.5). Stratified analysis suggested evidence of strong interactions between wood dust exposure and both mutagen sensitivity and smoking in lung cancer risk.