Six chemicals used as ingredients in cosmetics were evaluated for mutagenic activity in Salmonella typhimurium. Two of these ingredients, trans-4-phenyl-3-butene-2-one and 2,2',4,4'-tetrahydroxybenzophenone, were mutagenic in the presence of rat liver S-9 towards strains TA100 and TA1537 respectively. An impurity found in some cosmetic products, N-nitrosodiethanolamine, was mutagenic to S. typhimurium strains TA1535 and TA100 in the presence of hamster-liver S-9 but not rat-liver S-9.