During immunotherapy with wasp venom, levels of venom-specific IgE antibodies increase and then fall, whereas the concentration of IgG antibodies rises and then remains at a high level. Successful treatment is therefore associated with both increased concentrations of serum IgG and decreased serum IgE antibodies to venom. In this study we have investigated the possible role of auto-antibodies in inducing the decrease in serum IgE antibody. Levels of auto-anti-IgE were measured by a radioimmunoassay. Anti-IgE auto-antibodies were not generated during immunotherapy and there was no significant difference in the levels of anti-IgE auto-antibodies between patients whose venom-specific IgE antibody levels fell more than fivefold after immunotherapy and those patients in whom IgE antibody levels did not change significantly. We conclude that anti-IgE auto-antibodies do not play a part in IgE suppression induced by immunotherapy.