The effects of various phenolic compounds isolated from the rootbark of the mulberry tree on rat platelet cyclooxygenase and lipoxygenase products formed from (1-14C)arachiodonic acid were studied. Kuwanons G and H, sanggenon C, and mulberrofuran Q at concentrations of 10(-3) to 10(-4)M inhibited the formation of 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and thromboxane B2 (cyclooxygenase products); however, they increased the formation of 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) (a lipoxygenase product). Sanggenon D and mulberrofuran J at concentration of 10(-3)M inhibited the formation of HHT, thromboxane B2, and 12-HETE. Mulberrofuran G at a concentration of 10(-3)M inhibited the formation of HHT, thromboxane B2, and 12-HETE, while at 10(-5)M, it inhibited the formation of 12-HETE without affecting the formations of HHT and thromboxane B2. Kuwanon M and mulberroside A did not affect arachidonate metabolism in rat platelets.