Human platelets metabolize 8,11,14,17-eicosatetraenoic acid primarily into 12-hydroxy-8,10,14,17-eicosatetraenoic acid. Several other hydroxy acids were also produced in small amounts via an indomethacin insensitive pathway. Platelet cyclooxygenase metabolized this acid only into 12-hydroxy-8,10,14-heptadecatrienoic acid. It was not possible to detect any cyclic products even though vesicular gland cyclooxygenase metabolizes this (n-3) acid to 17,18-dehydroprostaglandin E1 (Oliw, E.H., Sprecher, H. and Hamberg, M. (1986) J. Biol. Chem. 261, 2675-2683).