Duration of venom immunotherapy still remains questionnable, since some patients outgrow their sensitivity. Two hundred venom-allergic patients (4 to 82 years; mean +/- SD, 37.3 +/- 14.2 years) who were first observed with systemic reactions (SRs) were investigated yearly for up to 3 years. Among these patients, 72 were allergic to honeybee venom, 83 to yellow jacket venom, and 45 to both yellow jacket and Polistes venom. At each visit patients had skin tests and RAST to venom. All patients had the same semirush protocol and a monthly maintenance dose of 200 micrograms. After 1 year of treatment, 19% of bee venom-allergic subjects and 35% of vespid venom-allergic individuals had a negative skin test and RAST to the corresponding venom. The percentage of negativation of tests increased after 3 years to 30.5% in bee venom-allergic patients and to 54% in vespid venom-allergic individuals. This rapid and relatively important negativation of skin tests and RAST may be due to a monthly maintenance dose of 200 micrograms; 76 patients experienced a field sting without any SR, two patients had a severe SR, and three patients had a mild SR. Although we tried to define parameters that might predict the abolition of venom sensitivity before starting immunotherapy, we could not find any parameter except venom species. Children and adults behave similarly in terms of evolution of venom sensitization. Mean serum venom-specific IgG levels were significantly lower in patients who had lost their sensitivity.