During the last 10 years, tremendous advances in the identification and characterization of allergens from a variety of substances have occurred. In this review, methods of allergen characterization and classification, as well as the effect of recent developments in biotechnology on allergen research, will be addressed. Prior to allergen isolation and characterization, adequate source material must first be identified. Most allergens that have been isolated are in the molecular weight range of 15,000 to 40,000 daltons and appear to be proteins or glycoproteins with acidic isoelectric points. A number of laboratory techniques have been shown to be extremely useful in identifying offending allergens and quantitating them in complex allergen extracts. Recently developed in vitro methods such as Western blotting, immunoprinting, and production of monoclonal antibodies to specific allergens will provide useful information for future analysis and standardization of allergen extracts. The effects of new technology on future developments in allergen characterization are far reaching. An important area of molecular biology that has only begun to be used in allergen research is the ability to clone and sequence DNA which codes for specific allergens. This facilitates the production of specific quantities of purified allergens provides material to determine their amino acid sequence, and allows production of standardized allergen preparations. Thus, it is conceivable that molecular biological approaches to allergen research will enable one to investigate the allergenic response at a molecular level and ultimately provide purified allergens in amounts sufficient for diagnosis and therapy.