Fungi from human environment or growing in human body may cause allergic reactions. The most common allergens are microfungi (moulds) belonging to imperfect fungi: Alternaria, Cladosporium and sack-like forms: Aspergillus, Penicillium and yeasts. Fungal antigens may stimulate production of specific IgE in atopic individuals what, as a rule, worsens the clinical course of atopic diseases: allergic sinusitis, bronchial asthma or atopic dermatitis. Fungi may also cause IgE-independent allergic reactions: by production of IgE, immunological complexes and by stimulating cell hypersensitivity. Whether allergic bronchopulmonary aspergillosis (ABPA), allergic fungal sinusitis (AFS) or allergic dermatitis appears, depends on the immunological state of human organism and exposure to fungal antigens.