The aim of the present research was to investigate the genotoxic potency of benzoyl peroxide (BPO), a whitener of flour and cheese, using in vitro sister chromatid exchange (SCE), chromosome aberration (CA), and micronucleus (MN) tests in human peripheral lymphocytes. Cells were exposed to 25, 50, 75, and 100 mu g/mL concentrations of BPO for 24 and 48 h. BPO induced SCEs only at the highest concentration (100 mu g/mL) for 48 h treatment. Furthermore, BPO induced CAs at 75 and 100 mu g/mL concentrations for 24 h treatment, and at all concentrations for 48 h treatment. BPO induced CAs in a dose-dependent manner for 24 and 48 h treatment periods. Increased level of MN formation induced by BPO was only observed for the 48 h treatment period at the 2 highest concentrations (75 and 100 mu g/mL). Statistically significant reductions in the proliferation index (PI) and mitotic index (MI) were only detected in cultures for the 48-h treatment period.