RS-37619 showed highly potent analgesic activity when given p.o. in tests utilizing underlying inflammation. It inhibited phenylquinone-induced writhing in the mouse and rat (350 and 180 x aspirin respectively) and the pain induced by flexing the adjuvant-inflamed rat paw (approximately 800 x aspirin). The agent increased the pain threshold of compressed yeast-inflamed rat paws (3-10 x naproxen). RS-37619 did not increase the pain threshold of the non-inflamed paw and was inactive in the mouse hot plate test; therefore it is probably not a centrally acting or morphine-like agent. RS-37619 was also highly active p.o. in rat models of acute and chronic inflammation. It inhibited carrageenan-induced paw edema (36 x phenylbutazone), cotton pellet-induced granuloma (less than or equal to 1 x indomethacin) and in an 18-day test, prevented the development of adjuvant-induced arthritis (approximately 2 x naproxen). RS-37619 exhibited antiphlogistic activity in adrenalectomized rats. It did not have corticosteroid activity. When given p.o., RS-37619 lowered yeast-induced pyrexia (20 x aspirin). Gastrointestinal irritation was seen in the rat with doses greater than or equal to 6.4 mg/kg/day p.o. The agent elicited mild CNS and cardiovascular activity only at doses far in excess of those required for analgesic and anti-inflammatory activity.