Arylamine N-acetyltransferase (NAT) plays an important role in the first step of arylamines metabolism. Luteolin has shown antibacterial, antioxidant and antineoplastic activity. To glean insights into the mechanism of action of luteolin, we assessed the effects of luteolin on NAT activity and gene expression and DNA-2-aminofluorene (AF) adduct formation in human bladder cancer T24 cells. By using high performance liquid chromatography, the amounts of N-acetylation of AF and DNA adducts were determined and quantitated. Gene expression was performed by using polymerase chain reaction and gel electrophoresis. The results indicated: 1) luteolin displayed a dose-dependent inhibition of NAT activity and gene expression (NAT1 mRNA) in T24 cells; 2) time-course experiments showed that N-acetylation of AF measured from intact T24 cells was inhibited by luteolin for up to 48 hours; 3) using standard steady-state kinetic analysis, it was demonstrated that luteolin was a possible uncompetitive inhibitor of NAT activity in T24 cells; and 4) the DNA-AF adduct formation in T24 cells was inhibited by luteolin. This report is the first finding which has shown luteolin to affect human T24 cell NAT activity and gene expression (NAT1 mRNA) and DNA-AF adduct formation.