The electroporation of restriction enzymes into mammalian cells results in DNA double-strand breaks that can lead to chromosome aberrations. Four chemicals known to interfere with cellular responses to DNA damage were investigated for their effects on chromosome aberrations induced by AluI and Sau3AI; in addition, the number of DNA double-strand breaks at various times after enzyme treatment was determined by pulsed-field gel electrophoresis (PFGE). The poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide (3AB) dramatically increased the yield of exchanges and deletions and caused a small but transitory increase in the yield of double-strand breaks induced by the enzymes. 1-beta-D-Arabinofuranosylcytosine, which can inhibit DNA repair either by direct action on DNA polymerases alpha and delta or by incorporation into DNA, potentiated aberration induction but to a lesser extent than 3AB and did not affect the amount of DNA double-strand breakage. Aphidicolin, which inhibits polymerases alpha and delta, had no effect on AluI-induced aberrations but did increase the aberration yield induced by Sau3AI. The postreplication repair inhibitor caffeine had no effect on aberration yields induced by either enzyme. Neither aphidicolin nor caffeine modulated the amount of DNA double-strand breakage as measured by PFGE. These data implicate poly(ADP-ribosyl)ation and polymerases alpha and delta as important components of the cellular processes required for the normal repair of DNA double-strand breaks with blunt or cohesive ends. Comparison of these data with the effect of inhibitors on the frequency of X-ray-induced aberrations leads us to the conclusion that X-ray-induced aberrations can result from the misjoining or nonrejoining of double-strand breaks, particularly breaks with cohesive ends, but that this process accounts for only a portion of the induced aberrations.