The present invention concerns the preparation of purified allergens and allergoids, both derived from whole bee venom, for the desensitization (immunotherapy) of subjects affected by a specific allergy. In particular, the present invention concerns a preparation for immunotherapy based on purified bee venom, characterized in that said bee venom is essentially mellitin-free. In addition, the preparation of a monomeric allergoid obtainable through the carbamylation or thiocarbamylation reaction of said mellitin-free bee venom, is described. Said allergoid, being characterized by reduced IgE-binding activity, may be a safer and more effective candidate for specific immunotherapy.