Abstract: The effect of tremulacin(TRC)extracted from Mao BaiYang(Folia Populustomentosa Carr)on actions of SRS-Aand histamine were investigated by using isolated guinea pigileumand spectrofluorometric assay.TRC was found to inhibit the contraction of isolated guinea pig ileuminduced by histamine and SRS-A,in a dose-dependent manner with IC50 of 1.78x10^-4 mol·L^-1and 2.51 X 1 0^-4mol·L^-1,reslpectively.TRC at the dose of 10^-4mol·L^-1 inhibited SRS-Arelease from sensitized isolated guine pig lung.While at the dose of l0^-5mol·L^-1 inhibited histaminerelease from the peritoneal mast cells in sensitized rats.These results indicate that in hibition of therelease of histamine and SRS-Amay play an important role in the mechanism of antiinflammatory actions of TRC.