To assess the genotoxicity of seven dental antiseptics, the ability of these agents to induce unscheduled DNA synthesis(UDS)was examined using Syrian hamster embryo(SHE)cells.Treatment of SHE cells with phenol or formaldehyde induced UDS in a concentration−dependent manner as determined by direct scintillation counting of [³H]thymidine incorporated into DNA during repair synthesis.Guaiacol or m−cresol induced UDS only in the presence of exogenous metabolic activation.p−Phenolsulfonic acid, sodium hypochlorite and p−chlorophenol failed to induce UDS in the presence or absence of exogenous metabolic activation.Our results suggest that phenol, guaiacol, m−cresol and formaldehyde are genotoxic to mammalian cells.