Isolated allergy to the common housefly (Musca domestica) has only been described in four cases. Predisposing factors include high concentrations of allergens and prolonged exposure time. Two pharmaceutical industry workers, 59 and 34 years of age, both without atopy, presented with recent onset of allergic rhinitis. Their symptoms appeared about 30 minutes after exposure to Musca domestica in the closed breeding rooms. They were symptom-free with other insects, on weekends and on vacation. Skin prick tests with common inhalant allergens were negative. Prick testing with crushed Musca domestica adults, hatched eggs, contaminated nets and sand, as well as fly feces were all positive. One patient had specific IGE antibodies against Musca domestica. Both patients lacked specific IgE antibodies against other insect species and common aeroallergens. In these two patients there was a species-specific sensitization without relevant cross reactions to other arthropods. The patients were transferred to new work sites where they had no contact with Musca domestica and became symptom-free. Thus this common insect can be a relevant occupational aeroallergen.