The genotoxicity of combinations of four p-oxybenzoic acids (methyl paraben, ethyl paraben, isopropyl paraben, butyl paraben) and benzoic acid had been evaluated. The in vitro Ames test using Salmonella typhimurium (TA 98, TA 100, 1535, TA 1537) and the invivo micronucleus assay using mouse peripheral blood were performed. Methyl paraben plus benzoic acid, ethyl paraben plus benzoic acid, and ethl paraben plus butyl paraben slightly increased the frequency of microuncleated reticulocytes in the high doses, but were negative in Ames test with Salmonella typhimurium with and without rat liver microsomal activation. The other combinations tested were negative in Ames test and did not show any clastogenic effect in micronucleus test. These results suggest that genotoxicity can produced by th combination of p-oxybenzoic acid.