Fungus is known to be one of the important causative allergens of allergic diseases such as bronchial asthma, allergic rhinitis and atopic dermatitis. Not only outdoor airborne fungi but also indoor fungi such as Aspergillus restrictus and Eurotium have recently received attention as causative fungal allergens of allergic diseases. In addition to careful history taking, in vivo testing methods such as skin test and conjunctival or bronchial provocation tests are sometimes necessary to diagnose the causative allergen. Problems requiring resolution are: 1. fungal allergens composed of multiple allergenic components, 2. difficulty of environmental monitoring of fungal allergens, 3. special characteristics as microorganisms, and 4. characteristics of normal flora allergy, etc.