Molecular approaches to allergen standardization include the development of purified natural or recombinant allergen standards whose structural and allergenic properties have been validated, in tandem with certified immunoassays for allergen measurement. Purified allergens can be used individually or incorporated into multiple allergen standards. Multicenter international collaborative studies are required to validate candidate allergen standards and immunoassays, as a prelude to being approved by regulatory agencies. Mass spectrometry is a sophisticated and powerful proteomics tool that is being developed for allergen analysis. Recent results using pollen allergens show that mass spectrometry can identify and measure specific allergens in a complex mixture and can provide precise information of the variability of natural allergen extracts. In future, the combined use of immunoassays and mass spectrometry will provide complete standardization of allergenic products. Molecular standardization will form the basis of new allergy diagnostics and therapeutics, as well as assessment of environmental exposure, and will improve the quality of treatment options for allergic patients.