Sixty-six patients with a history of systemic allergy reactions to bee stings, positive skin prick test to less than or equal to 100 micrograms/ml bee venom, and positive radioallergosorbent test (RAST) results were given venom immunotherapy. IgE and IgG antibodies to bee venom were measured by RAST and enzyme-linked immunosorbent test (ELISA), respectively. IgE and IgG anti-bee venom levels rose initially, but subsequently fell during immunotherapy. In 31 patients in whom specific IgE fell to low (less than 6% counts bound) or unmeasurable levels, immunotherapy was discontinued, and sting challenge was carried out 1 to 3 years later. All patients tolerated sting challenge well. The specific IgE and IgG antibody levels did not change significantly after treatment was stopped. Our data suggest that hyposensitization treatment can be stopped when specific IgE serum concentrations have fallen to low or unmeasurable levels and specific IgG antibody values are maintained, and that in a considerable number of patients venom immunotherapy has a lasting therapeutic and immunologic effect.