Some non-steroid anti-inflammatory drugs which inhibit arachidonate cyclo-oxygenease have been examined for their effects on leukocyte migration, prostaglandin production and oedema formation in carrageenin-induced inflammation in the rat. At doses which inhibited oedema, all the drugs tested caused a dose-dependent reduction in numbers of leukocytes and prostaglandin concentrations in 24-h inflammatory exudates. At lower doses, indomethacin, aspirin, sodium salicylate, flurbiprofen and phenylbutazone significantly potentiated leukocyte migration by 20-70%. Ibuprofen, naproxen and BW755C reversed the indomethacin-induced increase in leukocyte accumulation. BW755C inhibits the generation of chemotactic lipoxygenase products and it is possible that the effects of all these drugs on leukocyte migration are mediated through the lipoxygenase pathway of arachidonic acid metabolism.