In order to clarify the mechanism of action of chloroquine, pharmacological actions of the drug were studied in the resected intestine of guinea pig, inflammatory edema caused on the paw of rat and passive cutaneous anaphylaxis in guinea pig. 1) In the study of the resected intestine of guinea pig, anti-histamine action of chloroquine was noted by showing that the drug had complete antagonistic action against the intestinal contraction caused by histamine administration. While chloroquine did not show anti-serotonine action; contraction of the intestine by serotonine was not influenced at all by the drug administration. 2) In the study of making inflammatory edema on the paw of rat, chloroquine showed inhibitory effect to the edema caused by histamine administration. However, the drug showed scarcely inhibitory effect to the serotonine and dextran edema. Other signs of antinflammatory effct of chloroqine was demonstrated by such finding that remarkable anti-inflammatory inhibition was revealed by the drug administration to the edema caused by anti-serum allergic
inflammation. 3) Furthermore, chloroquine showed marked anti-allergic action on passive cutaneous anaphylaxis of guinea pig. Above mentioned pharmacological actions of chloroquine such as anti-histamine, anti-inflammatory and anti-allergic action as well as other actions of chloroquine such as relaxation of the smooth muscle, fibroblast-inhibiting action, inactivity of the antibody or improvement of general constitution are thought to be very important mechanism of actions to the treatment of bronchial asthma.