Cystic fibrosis patients often show sensitization to common indoor allergens, including fungi. Allergen exposure can exacerbate respiratory symptoms, including asthma. A 12 year old female patient with cystic fibrosis and asthma, and past ABPA, experienced asthma exacerbations at home. The patient tested positive by SPT to Der p 1, cat, and several fungal allergens. Airborne fungal exposure at home was suspected. 10M inhalable fraction air samplers were used in the home for 6 hours, staggered over a 24 hour period. Samples were cultured for fungal identification and viable counts. Samples were also immunostained for binding with the patient's serum IgE and with specific monoclonal antibodies (mAb), using the Halogen immunoassay (HIA). Viable counts reported 39 and 60 fungal CFUs in the bedroom and living room, respectively, from the 6-hour inhalable fraction air sample. Using HIA, 60 and 46 fungal conidia collected in the bedroom and living room, respectively, were seen to bind the patient's IgE. Similarly, IgE reactive hyphal counts were 6 and 8, whereas other antigenic particles were 176 and 214. Specific mAb HIAs showed 4056 (bedroom) and 3900 (living room) Fel d 1 particles, and 520 (bedroom) and 4660 (living room) Der p 1 particles. Using the HIA, we were able to determine what proportion of the airborne allergens in a home were contributed by fungal conidia and hyphae. In this case, the bulk of aeroallergen binding patient IgE was due to non-fungal sources. However, due to their viability, airborne fungal conidia may present greater potential allergen sources.