Monosodium urate crystal-induced inflammation was studied in an air pouch model of rat synovium. Phagocytosis of crystals by macrophage-like and fibroblast-like cells in the pouch lining was observed 30 minutes after crystal injection and preceded polymorphonuclear leukocyte accumulation. Levels of the prostaglandins PGE2 and 6-keto-PGF1 alpha, measured in serial pouch washouts, showed a clear temporal dissociation with leucocyte numbers, with peak levels of the prostanoids occurring before the maximum accumulation of leucocytes. Indomethacin abrogated prostaglandin synthesis completely without reducing leucocyte counts in pouch washouts. We propose that the pouch lining cells may be the primary source of the prostaglandins and these mediators do not have a significant role in leucocyte chemotaxis in this model.