Determination of the formation of thromboxane B2 (TxB2), 12L-hydroxy-5,8,10 heptadecatrienoic acid (HHT) and 12L-hydroxy-5,8,10,14 eicosatrienoic acid (HETE) from arachidonic acid and of the TxB2 :HHT, TxB2 :HETE and (TxB2 +HHT) :HETE ratio in human platelets. Possible use in diagnostic purposes.