Zanthoxylum ailanthoides is a medium to large-sized tree found at low altitude in forests of China, Korea, Japan, the Philippines, and Taiwan [1]. Its leaves are used as a folk medicine to treat the common cold in Taiwan [2]. Benzo[c]-phenanthridines, quinolines, coumarins, flavonoids, lignans, and terpenoids have been identified as constituents of this plant. Antiplatelet aggregation [3] and anti-HIV [4] activities have been reported for some of these compounds. In our studies on constituents of Formosan plants for in vitro inhibitory activity on neutrophil pro-inflammatory responses, Z. ailanthoides was found to be an active species. Five new compounds, ailanthamide (1), N-(4-methoxy-phenethyl)-N-methylbenzamide (2), (2E,4E)-N-isobutyl-6-oxohepta-2,4-dienamide (3), 4-(4′-hydroxy-3′-methylbut-oxy)benzaldehyde (4), and (E)-methyl 4-[4-(3-hydroxypropyl)phenoxy]-2-methylbut-2-enoate (5), and 17 known compounds have been isolated and identified from the stem bark of Z. ailanthoides. The structures were determined through spectroscopic and MS analyses. Compounds 1, 3, xanthyletin, decarine, (+)-episesamin, (-)-hinokinin, and evofolin-B exhibited inhibition (IC50≤ 5.34 µg/mL) of superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine/cytochalasin B (fMLP/CB). Compounds 1, xanthyletin, decarine, and (+)-episesamin also inhibited fMLP/CB-induced elastase release with IC50 values ≤ 5.53 µg/mL. Acknowledgements: This work was supported by a grant from the National Science Council of the Republic of China.References: [1] Chang, C.E. and Hartley, T.G. (1993) Rutaceae in Flora of Taiwan. 2nd edition. Editorial Committee of the Flora of Taiwan, Taipei, Taiwan, Vol. 3. [2] Gan, W. S. (1970) Manual of Medicinal Plants in Taiwan, National Research Institute of Chinese Medicine, Taiwan, Vol. II. [3] Sheen, W. S. et al. (1994) Phytochemistry 36:213–215. [4] Cheng, M. J. et al. (2005) Bioorg. Med. Chem 13:5915–5920.