Red wine and purple grape juice contain polymeric flavonoids with antioxidant properties believed to be protective against cardiovascular events but the alcohol and sugar content of these beverages has curtailed their medicinal use. Acute cardiac events are also associated with enhanced inflammation and thrombosis. In this study, the extracts from grape skins or seeds were examined for their anti-inflammatory properties and effect on platelet release of reactive oxygen intermediates. Incubation of platelets with seed or skin extract led to a decrease in platelet aggregation from 68.8+/-19.8% to 45+/-3.6% for seeds and to 27+/-7.2% for skin, respectively (P<0.05). Platelet incubation with grape skin or seed extracts led to a marked decrease in superoxide release from 73+/-6.2 to 2+/-3.4 for grape seeds and to 0.33+/-0.57 for grape skin (chemilum. units; P<0.05) as well as a significant increase in radical-scavenging activity, decrease in reactive oxygen species release by confocal microscopy, and enhanced platelet NO was measured using an NO-sensitive microelectrode. These effects were dose dependent for both grape extracts. Coincubation with seeds and skins led to additive inhibition of platelet aggregation, enhanced NO release, and prevented superoxide production. Incubation with seed or skin extracts led to an immediate attenuation of release of the inflammatory mediator, soluble CD40 ligand. Thus, the extracts from purple grape skins and seeds inhibit platelet function and platelet-dependent inflammatory responses at pharmacologically relevant concentrations. These findings suggest potentially beneficial platelet-dependent antithrombotic and anti-inflammatory properties of purple grape-derived flavonoids.