Arylamine N-acetyltransferase (NAT) plays an important role in the metabolism of 2-aminofluorene (AF) and some types of arylamine drugs and carcinogens. Our previous studies have demonstrated that paclitaxel decreases NAT activity in human bladder, blood, colon and lung cancer cells. In this study, paclitaxel was selected to test the inhibition of NAT activity (N-acetylation of AF) and NAT gene expression in a human bladder cancer cell line (T24). The NAT activity was determined by high performance liquid chromatography for measuring the levels of N-acetylation of AF. The data showed that a 24-hour paclitaxel treatment decreased the amount of N-acetylation of AF in T24 cells. The NAT enzymes were stained and analyzed by Western blotting and flow cytometry. The tests indicated that paclitaxel decreased the levels of NAT in T24 cells. The expression of the NAT gene (mRNAT NAT) was determined by polymerase chain reaction (PCR) and cDNA microarray and it was found that paclitaxel induced the down-regulation of mRNA NAT expression in T24 cells.