Antrafenine effectively suppressed carrageenan paw oedema in the rat (ED 40 = 24 mg/kg p.o) in the dose range of 10-40 mg/kg p.o, approximating that of phenylbutazone. Antrafenine was superior to phenylbutazone with respect to inhibition of exudate volume and total leucocyte infiltration in carrageenan and calcium pyrophosphate dihydrate crystal pleurisies. The effect of antrafenine on leucocytes was most striking, significant suppression being observed at each dose tested (10, 20, 40 mg/kg p.o), whereas phenylbutazone showed significant activity only at the relatively elevated dose of 40 mg/kg p.o. These observations suggest that antrafenine merits further investigation with respect to its anti-inflammatory effects.