The guinea-pig perfused isolated lung, used in conjunction with the cascade superfusion system to measure the release of thromboxane A2(TXA2), is a simple and convenient model for assessing the inhibition by glucocorticoids of eicosanoid formation1–8. Dexamethasone inhibits the release of TXA2 from the lung when it is stimulated by agents such as RCS-RF2 of leukotrienes,4,8 but not when bradykinin or arachidonic acid are used1–7. Using this model we have shown that the glucocorticoids suppress eicosanoid generation by cells through the induction of a family of phospho-lipase A2-inhibitory proteins5,6 now termed the 'lipocortins'9. Recently the primary structure of one form of lipocortin has been elucidated and the human gene cloned10. Lipocortin 1 is a polar monomeric protein with anti-phospholipase properties in vitro10,11 and we now report that when infused into guinea-pig lung preparations this protein has the same inhibitory profile as the glucocorticoids but with a more rapid onset of action. This is the first demonstration that eicosanoid formation can be inhibited by a recombinant phospholipase inhibitory protein applied extracellularly.