The design and laboratory evaluation of a new multi-stage aerosol sampler, incorporating an array of six 10-mm diameter cyclones operated in parallel at varying flow rates is described. Each cyclone samples from a common axial inlet tube at a different flowrate, and therefore, has a different characteristic particle size cut-off. The undersized particles are collected on filters. The particle size distribution of the ambient aerosol is determined from the sample masses on the back-up filters and a parallel filter which has no pre-collector. Since the cyclone efficiencies do not vary with loading, the sampling Intervals can be as long as necessary to obtain the desired sample masses.