The roots and rhizomes of Veratrum formosanum Losen (Liliaceae), a folk medicine, are used as an antihypertensive crude drug in Taiwan (1). In the course of our work on this plant in the search for bioactive principles, β-sitosterol (1), an antiplatelet agent, trans-resveratrol (2), and a steryl alkaloidal ester, angeloylzygadenine (3) were isolated from the roots and rhizomes of this plant. In this paper, we describe the characterization of 2 and 3 by means of more detailed spectroscopic studies and report the antiplatelet effect of 2. The antiplatelet effect of 2 was studied on the aggregation of the washed rabbit platelets induced by ADP (20μM), arachidonic acid (100μM), PAF (2ng ml⁻¹), and collagen (10μg ml⁻¹). The degree of the inhibitory effect was shown to be different depending upon the types of aggregation inducers. Compound 2 strongly inhibited platelet aggregation induced by arachidonic acid and also significantly inhibited those by ADP and collagen (Table 2). Since platelet aggregation caused by exogenous arachidonic acid was most easily inhibited by 2, the main antiplatelet effect of 2 may be due to inhibition of thromboxane A₂ formation (Table 3). The esterified 3 did not show any enhancement of its antiplatelet effect. Diseases caused by protozoa are responsible for a considerable mortality throughout the world, more particularly in the tropics. Few drugs are currently available to treat such infections and certain phenomena of resistance may even occur, leading to an urgent need for new selective agents (1). In this paper, we report the results of studies on diploceline, a quaternary alkaloid isolated from the root bark of Strychnos gossweileri Exell. (2). Previous works have shown that this alkaloid is devoid of cytotoxic activity (3) even at 200μg/ml, but has antimicrobial properties on Streptococcus species (S. haemolyticus) at a relatively high dose (0.5 mg/ml) (4). The discovery of antiparasitic activities in quaternary alkaloids, such as berberine and derivatives (1), led us to check whether diploceline was active against Entamoeba histolytica, Plasmodium falciparum, or Trichomonas vaginalis cultured in vitro. Furthermore, we also studied its mutagenic or antimutagenic effects (inhibition of the mutagenicity of both benzo[a]pyrene and smoker urine). The results indicate that diploceline is devoid of any mutagenic or antimutagenic effect at 2.5 mg/ml. Besides, it does not produce any inhibition of P.falciparum growth at 25 μg/ml (maximum tested concentration). Nevertheless, diploceline is active at 25 μg/ml on T. vaginalis and at 50 μg/ml on E. histolytica (Table 1). This activity is relatively weak as compared to metronidazole whose M.I.C. values in the same experimental conditions on E. histolytica and T. vaginalis