A linear theory of the loading of particulate filters with monodisperse aerosols can be developed by analogy with that for deposition of adsorbed material within vapour filters. The theory predicts that the aerosol penetration decreases approximately exponentially with time, and that the deposit decreases with depth at a quantifiably more rapid rate than exponential. The behaviour of the filter can be described in terms of the layer efficiency and a further constant, the mass of deposited aerosol per unit volume of filter that results in a doubling of the layer efficiency. Both parameters can be obtained from measurement of the penetration of the aerosol as a function of time, and experiments show that the same values give a reasonable fit to the observed spatial deposition pattern. Discrepancies observed are probably due to the presence of higher-order terms than linear.