The importance of fungal allergen products in the practice of clinical allergy is frequently underestimated. A wide variety of fungal species have been demonstrated to elicit allergic symptoms and to sensitize patients. The quality of fungal allergen preparations might have a significant effect on the specificity and sensitivity of diagnostic tests. Varying degrees of cross-reactivity have been shown among fungal genera, and the clinical relevance of this cross-reactivity has been neither fully appreciated nor applied to clinical practice. In addition, an increasing number of potentially new fungal allergen sources for which commercial extracts are not available are being identified. Manufacturers of allergen products have the formidable task of providing quality fungal allergen extracts that are routinely used for specific allergy diagnosis and treatment in the clinic. Currently there are no standardized fungal allergen products available in the United States because of inherent difficulties with manufacturing and standardizing fungal extracts. Without intervention, progress will not be forthcoming.