The aerobiology of molds and their products includes a significant contribution to human atopy.Alternariaallergens are numerous and vary qualitatively and quantitatively in extracts used for allergy diagnosis and immunotherapy. Progress in the isolation and characterization of these allergens is discussed, including a major acid allergen, Alt-1, and a low molecular weight basic allergen. The detection and characterization of human allergens from mycelial and spore extracts, as well as the demonstration of cross-reactivity among different mold species and genera, is also deemed important. A variety of techniques used in allergen research is described.