Anti-inflammatory and gastrointestinal ulcerogenic activities of zomepirac sodium were investigated in experimental animals. The inhibitory activity of zomepirac sodium against carrageenin hind paw edema in rats, acetic acid-induced increase in vascular permeability in mice, and UV-erythema in guinea pigs was more potent than that of indomethacin. Anti-edema activity of zomepirac sodium was seen in adrenalectomized rats. Zomepirac sodium, like indomethacin, inhibited the delayed phase of hind paw edema produced by mixed phlogistics, but not the early phase mediated by histamine and serotonin in rats. Zomepirac sodium produced a dose-dependent inhibition against granuloma formation, established adjuvant arthritis, and development of adjuvant arthritis in rats; and its activity was slightly less potent than that of indomethacin. The inhibitory activity of zomepirac sodium on PGE2 biosynthesis in vitro was about one-third that of indomethacin. The ulcerogenic activity of zomepirac sodium was about 5 times weaker than that of indomethacin. From these results, it was suggested that zomepirac sodium was effective on various types of inflammation and showed particularly potent inhibitory activity against acute inflammation. These findings suggest that the mode of action of zomepirac sodium is similar to that of other acidic non-steroidal anti-inflammatory drugs.