A new chemical compound, 11-oxo-11H-pyrido[2,1-b]quinazoline-2-carboxylic acid (Sm 857), known to have antiallergic activity was investigated with respect to its antiinflammatory effect. Sm 857 did not inhibit ultraviolet-induced erythema in guinea pigs, intradermal increased vascular permeability induced by histamine in rats and carrageenin-induced edema of the rat hind paw. Further, the compound showed no influence on wound healing in rats and was observed to exert neither analgesic nor inhibitory effect on platelet aggregation. Sm 857 was thus found to have no effect at all on acute and chronic inflammatory reactions. It was denied, therefore, that any antiinflammatory effect might be involved in the antiallergic effect of Sm 857 but it may be related to an inhibitory effect on the release of mediators or on some earlier stage. Therefore investigation was carried out into its inhibitory action on dextran- and compound 48/80-induced edema of the rat hind paw. As a result, Sm 857 showed a stronger inhibitory effect on dextran edema than tranilast. Sm 857 inhibited endotoxin-induced diarrhea in mice and the effect was similar to that of tranilast, suggesting its inhibitory action on the release of mediators.