We examined genotoxicity and DNA damage response in HepG2 cells following exposure to benzidine. Using the Comet assay, we showed that benzidine (50-200 mu M) induces DNA damage in HepG2 cells. DNA damage signaling pathway-based PCR arrays were used to investigate expression changes in genes involved in cell-cycle arrest, apoptosis, and DNA repair and showed upregulation of 23 genes and downregulation of one gene in benzidine-treated cells. Induction of G2/M arrest and apoptosis was confirmed at the protein level. Real-time PCR and Western blots were used to demonstrate the expression of select DNA repair-associated genes from the PCR array. Upregulation of the p53 protein in benzidine-treated cells suggests the induction of the p53 DNA damage signaling pathway. Collectively, DNA damage response genes induced by benzidine indicate recruitment complex molecular machinery involved in DNA repair, cell-cycle arrest, and potentially, activation of the apoptosis. Environ. Mol. Mutagen. 52:664-672, 2011. (C) 2011 Wiley Periodicals, Inc.