The effect of acteoside, a phenylpropanoid glycoside isolated from Clerodendron trichotomum Thunberg, on histamine and arachidonic acid release was investigated in RBL 2H3 cells. Histamine was dose-dependently released from RBL 2H3 cells by melittin, arachidonic acid and thapsigargin. In extracellular $Ca^{2+}-free$ solution, basal secretion of histamins increased by two fold. The response of histamine release to melittin and thapsigargin in $Ca^{2+}-free$ solution was significantly decreased, whereas the response to arachidonic acid was significantly increased as compared with those in normal solution. Acteoside inhibited histamine release induced by melittin, arachidonic acid and thapsigargin in a dose-dependent manner in the presence or absence of extracellular $Ca^{2+}$. However, the inhibitory activity of acteoside was more potent in normal solution than that in $Ca^{2+}-free$ solution. These data suggest that inhibitory mechanism of acteoside on histamine release may be related to extracellular $Ca^{2+}$. On the other hand, acteoside significantly inhibited arachidonic acid release and prostaglandin $E_2$ production Induced by $0.5;{mu}M$ melittin. It is possible that acteoside may be developed as an anti-inflammatory agent.