Five new compounds, ailanthamide (1), N-(4-methoxyphenethyl)-N-methylbenzamide (2), (2E,4E)-N-isobutyl-6-oxohepta-2,4-dienamide (3), 4-(4'-hydroxy-3'-methylbutoxy)benzaldehyde (4), and (E)-methyl 4-[4-(3-hydroxypropyl)phenoxy]-2-methylbut-2-enoate (5), and 17 known compounds have been isolated from the stem bark of Zanthoxylum ailanthoides. The structures were determined through spectroscopic and MS analyses. Compounds 1, 3, xanthyletin, decarine, (+)-episesamin, (-)-hinokinin, and evofolin-B exhibited inhibition (IC(50) < or = 5.34 microg/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 IC(50) values < or = 5.53 microg/mL.