A number of lines of evidence suggest that red wine may be more effective than other alcoholic beverages in decreasing the risk of coronary heart disease (CHD) mortality. This protection over and above that due to ethanol itself may be explained by phenolic components with which red wines are richly endowed. We have studied the effects of the trihydroxy stilbene trans-resveratrol on human platelet aggregation and on the synthesis of three eicosanoids from arachidonate by platelets, i.e. thromboxane B2 (TxB2), hydroxyheptadecatrienoate (HHT) and 12-hydroxyeicosatetraenoate (12-HETE). These effects were compared with the actions of other wine phenolics (quercetin, catechin and epicatechin) and antioxidants (alpha-tocopherol, hydroquinone and butylated hydroxytoluene). trans-Resveratrol and quercetin demonstrated a dose-dependent inhibition of both thrombin-induced and ADP-induced platelet aggregation, whereas ethanol inhibited only thrombin-induced aggregation. The other compounds tested were inactive. trans-Resveratrol also inhibited the synthesis of TxB2, HHT, and to a lesser extent 12-HETE, from arachidonate in a dose-dependent manner. Quercetin inhibited only 12-HETE synthesis, and hydroquinone caused slight inhibition of TxB2 synthesis, the remaining compounds being ineffective. De-alcoholized red wines inhibited platelet aggregation; their ability to inhibit the synthesis of TxB2 but not that of 12-HETE from labelled arachidonate by washed human platelets was proportional to their trans-resveratrol concentration. These results are consistent with the notion that trans-resveratrol may contribute to the presumed protective role of red wine against atherosclerosis and CHD.