We studied the inhibitory effect of the green sap of Ixeris dentata (IXD) on compound 48/80-induced anaphylaxis-like response in a murine model. IXD dose-dependently inhibited the anaphylaxis-like response induced by compound 48/80 in mice. IXD inhibited the anaphylaxis-like fatal response at the dose of 0.1 g/kg by 75%. IXD had a significant inhibitory effect on compound 48/80-induced ear swelling response at the doses of 0.05 and 0.1 g/kg. IXD (0.1 g/kg) also inhibited passive cutaneous anaphylaxis mediated by anti-dinitrophenyl IgE by 81.45%. When IXD was given as a pretreatment at concentrations ranging from 0.005 to 0.1 g/l, the histamine release from rat peritoneal mast cells induced by compound 48/80 was reduced in a dose-dependent manner. These results indicate that IXD may possess antianaphylactic activity.