A semisynthetic chemical compound, demethyldiisoeugenol, concentration dependently inhibited platelet aggregation and ATP release stimulated by thrombin (0.1 U/mL), platelet-activating factor (2 ng/mL), arachidonic acid (100 microM), collagen (10 micrograms/mL), and U46619 (1 microM) in rabbit washed platelets. The IC50 values of demethyldiisoeugenol on the inhibition of platelet aggregation induced by these five agonists were 157.3 +/- 22.3, 156.2 +/- 12.9, 53.6 +/- 4.7, 54.5 +/- 3.9, and 87.7 +/- 3.2 microM, respectively. Demethyldiisoeugenol also inhibited thromboxane B2 formation induced by thrombin, platelet-activating factor, arachidonic acid, and collagen, and prostaglandin D2 formation was induced by arachidonic acid. The rising intracellular Ca2+ concentration stimulated by these five platelet aggregation inducers was inhibited by demethyldiisoeugenol, while formation of inositol monophosphate was unaffected. Platelet cAMP and cGMP levels were unchanged by demethyldiisoeugenol. It is concluded that demethyldiisoeugenol may directly inhibit both intracellular calcium mobilization and cyclooxygenase activity in platelets.