Background: Vacuum cleaners may increase the level of airborne allergens by leakage through the cleaners or by disturbance of floor dust by the exhaust air produced. Objective: The aim of this study was to evaluate the short-term effect of vacuum cleaning with two different types of cleaners on airborne cat allergen analyzed by a biologic and by an immunochemical test. Methods: Ten homes with cats were cleaned in random order with a 1-week interval by a traditional canister type vacuum cleaner (T) and a semi- stationary vacuum cleaner (S) that conducts the air to the exterior through a valve in the wall. Airborne particles were collected by air sampling for 2 hours and cat allergen, Eel d 1, was quantified biologically by basophil histamine release test (HR test) and immunochemically by enzyme linked immunosorbent assay (ELISA). Results: Using the S resulted in smaller amounts of airborne cat allergen than the T (mean 2.1 ng/m³ air (range .8 to 12.5) versus 5.2 ng/m³ (1.3 to 13.3), P < .002 measured by ELISA). Results from ELISA and HR test correlated well (r = .91, P < .001). Conclusions: The use of S with exhaust to the outside of the dwelling gave rise to less airborne low particle size allergen during the cleaning procedure than a T method. The basophil histamine release test could be a valid alternative method to establish allergen content in environmental samples especially in allergen systems with no available monoclonal antibodies.