['To investigate if formocresol, paramonochlorophenol, or calcium hydroxide modulate the genotoxic effects induced by the oxidatively damaging agent hydrogen peroxide (H2O2) or the alkylating agent methyl methanesulfonate (MMS) in vitro by using single cell gel (comet) assay.', 'Chinese hamster ovary (CHO) cells in culture were exposed directly to formocresol, paramonochlorophenol, or calcium hydroxide (adjusted to 100 microg/mL) for 1 hour at 37 degrees C. Subsequently the cultures were incubated with increasing concentrations (0-10 micromol/L) of MMS in phosphate-buffered solution (PBS) for 15 minutes at 37 degrees C or of H2O2 at increasing concentrations (0-100 micromol/L) in distilled water for 5 minutes on ice. The negative control cells were treated with PBS for 1 hour at 37 degrees C. The parameter from the comet assay (tail moment) was assessed by the Kruskal-Wallis nonparametric test followed by a post hoc analysis (Dunn test).', 'Clear concentration-related effects were observed for the genotoxin-exposed CHO cells. Increase of MMS-induced DNA damage was not significantly altered by the presence of the compounds tested. Similarly, no significant changes were observed when hydrogen peroxide was used with the endodontic compounds evaluated.'] Do antimicrobial endodontic compounds modulate alkylation-induced genotoxicity and oxidative stress in vitro?