Four compounds, including one benzenoid, 4-O-methylgallic acid (1), together with three arylnaphthalide lignans, namely phyllamyricin C (2), justicidin B (3) and diphyllin (4) were isolated from the whole plants of Phyllanthus polyphyllus L. (Euphorbiaceae). This was the first isolation report of compounds 1-4 from this plant species. The in vitro inhibitory effects of these compounds were evaluated on the production of nitric oxide (NO) and cytokines (tumor necrosis factor (TNF)-alpha and interleukin (IL)-12), from LPS/IFN-gamma activated murine peritoneal macrophages. The results indicated that the 50% inhibition concentration (IC(50)) values of NO production from activated peritoneal macrophages by compounds 1-4 were 100, 25, 12.5 and 50 microM, respectively. In parallel, these dilutions were approximately inhibited in a similar manner to that observed for cytokines (TNF-alpha, and IL-12) production. On the other hand, at 100 microM concentration compounds 3 and 4 showed 50% inhibition of NO production from peritoneal macrophages that had been pre-activated with LPS/IFN-gamma for 24h, whereas compounds 1 and 2 inhibited only about 20 and 10%, respectively. These results support the use of this plant for the treatment of inflammatory diseases in oriental traditional medicine.