The effects of 3-aminobenzamide (ABA), a representative inhibitor of poly(ADP-ribose)polymerase, on the induction of gamma-glutamyl-transpeptidase (GGT)-positive foci, an early lesion occurring during hepatocarcinogenesis, in rat liver by various chemicals were studied in Fischer 344 and Wistar rats. ABA exhibited an enhancing effect on the induction of GGT-positive foci by benzo[a]pyrene, but no effects on induction by a methylating agent, N-methyl-N-nitrosourea, in both rat strains. In contrast, the induction of GGT-positive foci by another methylating agent, 1,2-dimethylhydrazine, was enhanced by ABA in Wistar rats, but not affected in Fischer rats. There were no effects of ABA on the induction of GGT-positive foci by N-bis(2-hydroxypropyl) nitrosamine in Wistar rats. These results indicate a differential effect of ABA on the induction of GGT-positive foci by different chemicals in different rat strains.