A dozen acetoxy benzene derivatives (mono- or diacetylated diphenols) were tested for inhibitory activity on platelet aggregation in human platelet rich plasma induced with collagen, ADP and arachidonic acid. All the compounds tested showed an activity, and the results emphasize the antiaggregant properties of diacetylated derivatives which are more potent than aspirin. Unlike aspirin, their action is not prevented by salicylate. However, the large inhibition of serotonin release and thromboxane synthesis localizes their activity in arachidonic acid metabolism.