Abstract Allergens produced by recombinant DNA technol-ogy have the ability to improve allergy diagnosis and are used as reference standards for analytical methods. In addition, the use of recombinant aller-gens in specic immunotherapy has long been con sidered potentially superior compared with the use of conventional extracts. e advantages are clear: a complex natural substance that is dicult to char-acterize is replaced by only those components rele-vant for treatment, which furthermore can be re-produced in pharmaceutical quality. e challenges faced here include selecting the relevant allergen molecules and establishing a manufacturing that meets all the regulatory requirements for marketing authorization. In addition to unmodied recombi-nant allergens, hypoallergenic variants with lower IgE reactivity can also be made by genetic engineer-ing. Proof of concept has been demonstrated for both these approaches in clinical trials