Allergic desensitization is still a subject of controversy. Several controlled studies have demonstrated its efficacy in allergy to hymenoptera venoms and in hayfever; results obtained in hypersensitivity to house dust mites, animal danders and molds are still controversial and those obtained with mixtures of various allergens and bacterial extracts have been most often negative. In the 80's, a new type of allergen preparation has become available in which the allergen content (and not only the protein content) is well determined ("standardized extract"). The use of this new type of preparation should allow a better quantitative approach to allergologic investigations, which are very useful for assessment of the desensitization value.