Arylamine N-acetyltransferase (NAT) activity in Helicobacter pylori was inhibited by ellagic acid, a possible chemopreventive drug. The NAT activity was determined using an acetyl CoA recycling assay and high pressure liquid chromatography. Inhibition of growth studies using H. pylori demonstrated that ellagic acid elicited a dose-dependent bactericidal effect in H. pylori cultures, i.e. the greater the concentration of ellagic acid, the greater the inhibition of growth of H. pylori. The IC50 value was 1 mM for inhibition of growth of H. pylori. Cytosols or suspensions of H. pylori with and without selected concentrations of ellagic acid co-treatment showed different percentages of 2-aminofluorene and p-aminobenzoic acid acetylation. The data indicated that there was decreased NAT activity associated with increased ellagic acid in H. pylori cytosols and intact cells. For the cytosol and intact bacteria examinations, the apparent values of K(m) and Vmax decreased after co-treatment with 1 mM ellagic acid. This report is the first demonstration of ellagic acid inhibition of arylamine NAT activity and ellagic acid inhibition of growth in the bacterium H. pylori.