The Chinese tallow tree [Sapium sebiferum (L.) Roxb., Euphorbiaceae], a species native to the People's Republic of China now naturalized in the southeastern United States, is of considerable interest as an economic plant (1,2). Following our previous isolation of the new natural product, 5,6,7,8-tetramethoxycoumarin, and other coumarins from the bark and roots of S. sebiferum (3), we now wish to report the identification of six constituents of the leaves of this species, several of which are of known biological activity. Other workers have isolated ellagic acid, friedelin, sitosterol, and three phorbol esters from this plant part (4,5). In the present investigation, a CHCl3-soluble fraction of an MeOH extract of the leaves of the Chinese tallow tree was found to display significant in vitro activity against the P-388 lymphocytic leukemia test system when assessed using standard protocols (6). Phorbol esters, which have previously been shown to possess activity in this test system (7), were shown by application of a skin-irritancy test (8) to be absent from the plant sample studied in this investigation. Cytotoxic activity was traced by activity-guided fractionation to the S. sebiferum constituent, gallic acid, which exhibited an ED50 of 0.7 μg/ml in the P-388 cell culture system. This compound has previously been found to show inhibitory activity against KE3 (9,10) and HeLa (11) cells but to be inactive when tested in vivo in the P-388 lymphocytic leukemia system over the dose range 50-200 mg/kg (9). Other compounds obtained in this study were astragalin, (-)-loliolide, kaempferol, quercetin, and β-sitosterol glycoside, none of which was found to be significantly cytotoxic to P-388 cells. However, astragalin is reported to have in vivo P-388 activity (12), and (-)-loliolide is a potent ant-repellent (13).