When 50 nmol of 14C-arachidonate was injected into the pulmonary circulation of isolated hamster lungs, the perfusion pressure was increased. This increase was not changed when sulfinpyrazone was infused into the pulmonary circulation at 20 mumol/l. Neither was the total amount of radioactivity in the effluent changed by sulfinpyrazone. The metabolites of arachidonic acid were analyzed from the nonrecirculating perfusion effluent, which was extracted with ethyl acetate first at neutral pH and then at pH 3.5. The only significant change in the metabolite formation was a small decrease in the amount of one metabolite extracted at neutral pH (obviously 12-hydroxy-5,8,10-heptadecatrienoic acid). The amounts of other metabolites, including 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and TxB2 were unchanged. The present study indicates that the pulmonary metabolism of arachidonic acid is changed only slightly by sulfinpyrazone.