In the Chinese medicine, Scutellaria baicalensis GEORG has been used as a remedy for some of allergic diseases. Therefore, the authors investigated the effects of baicalin and baicalein, components of the drug, on active anaphylactic reaction in guinea pig, and the results obtained were compared with those of rutin, methylhesperidin and quercetin. 1) By the administration of baicalin, the onset of preconvulsion caused by the antigen-aerosol in actively sensitized guinea pig was delayed about 3 times in contrast to the control, and the effect of baicalin was more potent than that of rutin. 2) Baicalin and baicalein inhibited Schulz-Dale reaction in isolated ileum, and the intensity of inhibition was following order; in glycoside, baicalin>rutin>methylhesperidin, and in aglycon, baicalein>quercetin. Futhermore, the effect of aglycone was more potent than that of each glycoside. 3) As the antigen was added to the organ bath which placed sensitized and non-sensitized ileum, sensitized ileum strongly contracted followed by contraction of non-sensitized one. In this condition, baicalin decreased the contraction of non-sensitized ileum, while baicalein strongly decreased those of both ones. 4) Baicalin and baicalein slightly showed antihistaminic and anticholinergic effects on ileum of guinea pig. 5) The antigen-antibody combination was not affected by baicalin or baicalein in ring precipitation test. 6) The release of histamine and SRS-A from sinsitized guinea pig lung which perfused with antigen were decreased by baicalin, and the decreasing activity was more remarkable than that of rutin. 7) Baicalin and baicalein inhibited the anaphylactic release of histamine and SRS-A from chopped tissue of guinea pig lung. There was not much difference between the inhibitory activities of them in a equal molar concentration. However, they neither affected the destruction of mediator released nor inhibited contraction of ileum by mediator. The inhibitory action of baicalein on release of mediator was not affected by the addition of Ca++, but decreased by cysteine.