The effect of 3-aminobenzamide (3AB), an inhibitor of polyadenosine diphosphoribose polymerase, on chromosome aberrations induced by ethyl methanesulfonate (EMS) or bleomycin (BLM) were investigated in Chinese hamster ovary cells at various stages of cell cycle. 3AB (5mM) alone did not affect the frequencies of chromosome aberrations over controls. The frequencies of chromosome aberrations by EMS were increased during late G₁ and early S phases. BLM showed the stage sensitivity to chromosome aberrations in G₂ phase. Post-treatment with 3AB did not affect the frequencies of chromosome aberrations induced by BLM in all stages and induced by EMS in mid S and G₂ phases.