Chromium　contaminated　drug　capsules　drew　much　of　world＇s　attentions.　Although　trace　amount　of　chromium　allowed　to　existence　in　the　drug　capsules,　but　the　combined　effects　of　chromium　with　other　drug　chemicals　remain　unclear.　Therefore,　the　combined　genotoxicity　of　hexavalent　chromium　[Cr　(VI)]　with　nitroso　drug　chloroethylnitrosourea　(ACNU)　was　examined　using　the　Salmonella　mutagenicity　assay.　The　results　showed　that　Cr　(VI)　and　ACNU　produced　a　dose-dependent　increase　in　the　revertants　in　TA　98　and　TA　100　strains.　In　the　individual　chemical　mutation　assay,　the　positive　mutagenicity　response　for　Cr　(VI)　doses　was　above　2　mg　per　plate,　and　for　ACNU　above　5　mg　per　plate.　In　binary　chemical　mutation　assay,　the　straightforward　positive　results　could　even　be　detected　when　the　dose　of　Cr　(VI)　and　ACNU　both　down　to　1　mg　per　plate.　It　was　indicated　that　neither　Cr　(VI)　nor　ACNU　individually　caused　more　genotoxicity　to　bacterial　DNA　at　low　levels.　However,　the　two,　working　together,　had　significant　revertant　mutation　effects.　This　means　the　combined　genotoxicity　effects　of　Cr　(VI)　and　ACNU　are　more　harmful　than　the　individual　exposure.