Although lung cancer risk did not increase significantly for GSTM1 null for either sex in the multivariate analysis, the effect of the CYP1A1 polymorphism may be stronger in GSTM1 null females (OR 6.54 in women, 95% CI 1.1–40.0 vs. 2.36 in men, 95% CI 0.49–11.49), independent of age or smoking history. The gene discussed is CYP1A1; the disease is lung cancer.