Fifteen stilbenoids and two alkaloids from Stemona collinsae, S. tuberosa, and S. peirrei were tested alongside the commercially available stilbenoids resveratrol and pinosylvin for inhibition of leukotriene formation in an ex vivo test system based on activated human neutrophilic granulocytes. The stilbenoids resveratrol (1), pinosylvin (2), dihydropinosylvin (3), stilbostemin A (4), stilbostemin B (5), stilbostemin D (6), stilbostemin F (7), stilbostemin G (8), stemofuran B (9), stemofuran C (10), stemofuran D (11), stemofuran G (12), stemofuran J (13), stemanthrene A (14), stemanthrene B (15), stemanthrene C (16), and stemanthrene D (17) showed structure-dependent activities with IC(50) values ranging from 3.7 to >50 microM. The alkaloids tuberostemonine (18) and neotuberostemonine (19) were inactive at a concentration of 50 microM.