The aim of the present study was to evaluate the antileukemic activity of six chemical classes of pure compounds present in commonly used medicinal plants in Taiwan--such as the genus Plantago. Studies were conducted on a series of human leukemia and lymphoma cell lines. Results showed that water soluble compounds (aucubin, caffeic acid, chlorogenic acid, ferulic acid, p-coumaric acid and vanillic acid) exhibited a weak antileukemic activity (IC50: 26-56 microg/ml, SI: 2-11). On the other hand, water insoluble compounds such as triterpenoids (oleanolic acid and ursolic acid), monoterpene (linalool) and flavonoid (luteolin) possessed strong activity against human leukemia and lymphoma cell lines. Among them, linalool showed the strongest activity against histiocytic lymphoma cells U937 (IC50: 3.51 microg/ml, SI: 592.6) and Burkitt lymphoma cells P3HR1 (IC50: 4.21 microg/ml, SI: 494.1). Ursolic acid was effective against P3HR1 cells (IC50: 2.5 microg/ml, SI: 262.6) and chronic myelogenous leukemia cells K562 (IC50: 17.79 microg/ml, SI: 36.91), whereas oleanolic acid inhibited the growth of P3HR1 cells (IC50: 26.74 microg/ml, SI: 11.37). Luteolin exhibited effective activity against K562 cells (IC50 18.96 microg/ml, SI: 5.14) and P3HR1 cells (IC50: 18.99 microg/ml, SI: 5.13). We conclude that terpenes and flavonoid in commonly used medicinal plants possess strong activity against lymphoma and leukemia cells, especially human lymphoma cells, suggesting the potential use of these compounds for treatment of lymphoma.