Concur-rent size-resolved measurements of airborne cat allergen (Fel d 1) and total particulate matter (PM) were collected in an experimental chamber for the first 5 min following a typical dust-generating household activity (vacuuming a carpet). Three different heights representative of typical elevations for human exposure were measured to assess vertical variations. Experiments showed that only a limited amount of deposited house dust is available for resuspension; the reservoir of dust in the carpet appears to become substantially depleted after about 3 iterations of a resuspension activity, and vertical variations in large PM (aerodynamic diameters > 10 mu m) become less pronounced. Measured removal rates of PM suggested that the average density of house dust may be substantially less than 1.0 g/cm(3). The allergenic content of the resuspended house dust was found to range between 0.03-0. 10%, with a preliminary suggestion of somewhat higher Fel d I levels in the submicron size range particles. (c) 2004 Elsevier Ltd. All rights reserved.