Bufezolac is a non-steroidal anti-inflammatory drug (NSAID). In the mouse, BUFEZOLAC was 30 times less active than indomethacin in Koster's test, but it was 13 times less toxic than the reference drugs. Bufezolac appeared to be as active as indomethacin in the various tests performed: Randall and Selitto's test for analgesic activity, hyperthermic rat, experimental models of inflammation (UV erythema, carrageenin-induced oedema, cotton granuloma, adjuvant-induced arthritis). In vitro, its inhibition of prostaglandin-synthetase in the guinea-pig lung was appreciably more powerful than that of indomethacin. Like all potent non-steroid anti-inflammatory drugs it has ulcerogenic activity, similar to that of indomethacin, which accounts for its acute oral toxicity in the rat. The activity Bufezolac is either the same as (antipyretic action) or inferior to (analgesic and anti-inflammatory activity and inhibition of prostaglandin-synthetase) that of indomethacin, but always markedly superior to that of phenylbutazone.