DNA single-strand breaks (DNA SSB) in peripheral lymphocytes of wooden furniture workers and a control group, including smokers and nonsmokers, were detected by the microfiltration method. Our results show that cigarette smoking significantly increases the fragmentation of DNA single strands in the wooden furniture workers (by nearly two times) but not in the control group. Moreover, occupational exposure to wood dust and other wooden plant substances significantly induced DNA SSB only in the lymphocytes of smokers (by about two times). DNA repair in the lymphocytes was investigated as 3H incorporation into DNA. High 3H incorporation in the unstimulated lymphocytes of both smoking and nonsmoking workers, as compared to the references, suggests that besides DNA SSB other DNA damage can be caused by occupational exposure in the wooden plant. Since DNA repair is not always perfect, the possibility is high that the low level of DNA repair in the study group may lead to irreversible DNA damage. We think that the workers exposed to wood dust and the substances emitted by furniture coating materials in the plant may be at higher risk for mutagenesis and/or carcinogenesis than the unexposed population.