Chironomidae larvae and midges cause allergic reactions in approximately 20 percent of exposed people; predominantly aquarists using insect larvae as fish food and environmentally exposed subjects living in areas abounding in water are affected. Our studies include 642 subjects of whom 205 are aquarists; 85 are occupationally and 352 environmentally exposed people. 123 of them were shown to be sensitized to these insects. Using highly purified allergens, we could demonstrate that Chironomidae hemoglobins (Chi t I) represent the major allergenic components causing rhinitis, conjunctivitis and bronchial asthma. Considerable immunological cross-reactivity exists between hemoglobins of the same and closely related Chironomidae species. Genetic factors seem to be important for the susceptibility of this type of allergy. In studies with peptides of Chi t I component III, we identified several epitopes recognized by human IgE antibodies and/or T-cells.