The inhibitory activity of cardamom extract was studied on human platelets. Platelet aggregation and lipid peroxidation were evaluated with platelet rich plasma (PRP) and platelet membranes, respectively, obtained from blood of healthy volunteers. Human platelets were subjected to stimulation with a variety of agonists including ADP (2.5 mM), epinephrine (2.5 mM), collagen (10 mM), calcium ionophore A 23187 (6 microM) and ristocetin (1.25 microg/mL). The IC50 were 0.49, 0.21, 0.55 and 0.59 mg with ADP, epinephrine, collagen and calcium ionophore A 23187, respectively, and no inhibition with ristocetin. The inhibitory effect was dose dependent with concentrations varying between 0.14 and 0.70 mg and time dependent at IC50. Lipid peroxidation induced by iron--ascorbic acid system in platelet membranes was analysed with malondialdehyde (MDA) as an index. An increase in concentration of cardamom has decreased the MDA formation significantly. Hence, it may be said that aqueous extract of cardamom may have component(s), which protect platelets from aggregation and lipid peroxidation.