The experimental asthma caused by IgE antibody in rats was inhibited by HSR-6071 (6-(1-pyrrolidinyl)-N-(1H-tetrazol-5-yl)-2-pyrazinecarboxamide) (0.01-0.1 mg kg-1 i.v.) in a dose-dependent manner. The inhibitory activity of HSR-6071 was more potent than those of disodium cromoglycate and ketotifen, and equipotent with amlexanox. The bronchoconstriction mediated by IgE or IgG antibody in guinea-pigs was also prevented by HSR-6071 (0.3, 1 and 3 mg kg-1 i.v.), amlexanox (3, 10 and 30 mg kg-1 i.v.) and ketotifen (0.1 mg kg-1 i.v.) but not by disodium cromoglycate (10 mg kg-1 i.v.). HSR-6071 was more potent than amlexanox, but less potent than ketotifen. HSR-6071 suppressed antigen-induced histamine and SRS-A release from minced lung tissues of guinea-pigs sensitized passively with rabbit anti-EA serum and was a more potent inhibitor of the release of SRS-A than of histamine. On the other hand, histamine- or acetylcholine-induced bronchoconstriction in guinea-pigs was scarcely affected by HSR-6071 at doses sufficient to inhibit the experimental asthma, but LTD4-induced bronchoconstriction was dramatically inhibited. These results indicate that the inhibitory action on experimental allergic asthma of HSR-6071 may be due to suppression of antigen-induced histamine and SRS-A release from lung tissues and to antagonism of SRS-A action. In addition, HSR-6071 inhibited cyclic AMP phosphodiesterase activity and produced relaxation of the guinea-pig isolated trachea. These pharmacological actions may contribute to the production of the anti-allergic action of HSR-6071.