Honeybee venom allergens modified by formaldehyde treatment (F), acetoacetylation (A), and coupling to polyethylene glycol (P) were studied with regard to their immunogenicity and their IgE-suppressive potential in rabbits and mice. F induced a strong IgG response in rabbits and especially mice, but only a moderate IgE response in the mouse. Its IgE-suppressive potential in mice was comparable to that of unmodified bee venom. A induced only a weak IgG and IgE response. Its IgE-suppressive potential was greater than that of unmodified bee venom. P was nonimmunogenic and had only a marginal IgE-suppressive effect. F and A seem promising for the treatment of bee sting-allergic individuals.