Detection of IgE antibodies specific to honeybee or Vespula venoms is an important criterium firstly for the diagnosis of sensitization and secondly for the indication for a specific immunotherapy. Some authors recommend to postpone blood analysis after an insect sting for a certain time because circulating IgE antibodies might be consumed by the allergic reaction, which would result in a false-negative test outcome. We investigated IgE concentrations during the first weeks after an insect sting in 31 patients with an unequivocal history of an anaphylactic reaction after a honeybee (n = 13) or Vespula (n = 18) sting. Blood samples for analysis of specific IgE concentrations (CAP system, Pharmacia Diagnostics, Sweden) were collected within 2 weeks and 5+/-2 weeks after the insect sting. 12/13 patients with honeybee venom and 14/18 patients with Vespula venom sensitization had CAP classes 1 or higher within the first 2 weeks. Those 5 patients with CAP class 0 within the first 2 weeks had detectable IgE concentrations a few weeks later. We conclude that testing for specific IgE to hymenoptera venoms is in most cases useful even during the first 2 weeks after the hymenoptera sting. This allows early decisions on further diagnostic procedures and the therapeutic way to choose. Patients with no detectable IgE should, however, be retested after a few weeks.