The joint effect of smoking and ABCB1 SNPs significantly increased the risk of CML; therefore, the smoker subjects with c.1236TT/CT and c.1236CC genotypes showed higher risk for CML development (six and five folds more than reference group; OR = 6.04; 95% CI: 2.82-12.92; p = 0.00 and OR = 4.95; 95% CI: 1.62-15.13; p = 0.005, respectively). The gene discussed is ABCB1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.