Twenty-four lipsticks of various shades and colors were tested for mutagencitiy with the histidine-requiring tester strain Salmonella typhimurium TA98. Nine lipsticks were mutagenic without microsomal (S-9) activation. Dose-response effects were observed. Eight colorants listed as ingredients of the mutagenic lipsticsk were tested with and without S-9. Drug and Cosmetic (D&C) Orange No. 17, a monoazo dye with two nitro groups, was highly mutagenic in the absence of S-9. The mutagenic effect was decreased or lost in the presence of S-9 prepared from livers of male noninbred Sprague-Dawley rats given a single injection of Aroclor 1254. Eight lipsticsk matched for ingredients other than dyes were tested. Two containing D&C Orange No. 17 were directly mutagenic. The mutagenic effect was decreased by the presence of S-9. Only D&C Orange No. 17 was sufficiently mutagenic without microsomal activation to account for the mutagenicity observed in these lipsticks. Lipsticks containing D&C Orange No. 17 and those labeled with the words "may contain" D&C Orange No. 17 should be suspected of being mutagenic for S. typhimurium TA98. This dye and 2,4-dinitrosaniline, which may also be present, are potential health hazards. Assessment of their carcinogenicity awaits evaluation of results obtained by appropriate testing in animals.