Probenecid [57-66-9] and bromcresol green (BGr) [76-60-8] reported to be prostaglandin transport inhibitors, were tested for their effectiveness in modifying the vasopressor responses to arachidonic acid Na salt (AA) [6610-25-9], 11-9 EM [56985-40-1], an endoperoxide analog, PGF2α tromethamine salt (I tromethamine salt) [38562-01-5], and norepinephrine [51-41-2] in the isolated perfused canine lung lobe.Only the pulmonary pressor action of AA was blocked by pretreatment with indomethacin.Probenecid attenuated AA responses and blocked those of I in a dose-related manner.BGr had no antagonistic activity against AA and inhibited I action by 50%.Probenecid and BGr appeared to inhibit differently.Neither blocked the pressor action of the endoperoxide analog, and neither attenuated the norepinephrine pressor action at prostaglandin inhibiting concentrationsThe use of organic acid transport inhibitors represents a potentially useful approach in studying the mechanisms of action of AA and its metabolic products.