Two new series of 2-arylmethyl-1,4-benzoquinones (2 and 3) were synthesized for evaluation of their pharmacological activities. These compounds showed significant inhibition of platelet aggregation and some of them possessed a protective against endothelial cell injury. Structure-activity relationship studies indicated that 2b, 2d and 3b are potent inhibitors of platelet aggregation induced by arachidonic acid (AA) with an IC50 in the range of 1-10 micrograms/ml. Among them, 3b showed a significant inhibitory activity against endothelial cell injury caused by hydrogen peroxide (H2O2) at 1 microM.