15-Hydroxyprostaglandin dehydrogenase (15-PGDH) catalyzes NAD(+)-dependent oxidation of 15(S)-hydroxyl group of prostaglandins and has been considered a key enzyme involved in biological inactivation of prostaglandins. This enzyme is markedly induced by androgens in hormone-sensitive human prostate cancer cells (Tong M., Tai H. H. Biochem Biophys Res Commun 2000; 276: 77-81) and may be involved in tumorigenesis. Inhibition of this enzyme may be of value in anticancer therapy. Non-steroidal anti-inflammatory drugs (NSAIDs) which inhibit cyclooxygenases (COXs) have been shown to be chemopreventive in epidemiological and animal-model studies. However, chemoprevention by these drugs may not be directly related to their inhibition of COXs. Other targets may be also involved in their chemopreventive activity. We have examined a variety of NSAIDs including COX-2 selective inhibitors, peroxisome proliferator-activated receptor (PPAR) gamma agonists and phytophenolic compounds which have been shown to be chemopreventive for their effect on 15-PGDH. It was found that most of these compounds were potent inhibitors of 15-PGDH. Among these compounds, ciglitazone appeared to be the most powerful inhibitor (IC(50)=2.7 microM). Inhibition by ciglitazone was non-competitive with respect to NAD(+) and uncompetitive with respect to PGE(2).