In a series of 102 patients consulting for allergic reactions following hymenoptera sting, fifty-two of them, who had experienced one or more severe systemic adverse reactions were selected for rush immunotherapy. The method employed made it possible to attain the maintenance dose of 100 micrograms of venom in 3 days. Patient tolerance was excellent, no serious side-effect was observed; immunotherapy never had to be stopped. Clinical effectiveness seems to be very satisfactory, since no abnormal reaction was reported in seven patients who later were spontaneously stung, and in fourteen patients who received an induced insect sting. The level of IgG antivenom antibodies rose regularly from the first month onwards to remain at a stable level. Because of its safety and effectiveness, it appears that this method should be recommended for immunotherapy in patients who are allergic to hymenoptera stings.