The parallel stage impactor segregates airborne particles according to their aerodynamic equivalent diameters without the errors usually associated with cascade impactors: particle bounce, blow-off and interstage loss. By using this impactor not only can the particle size distribution be determined, but the sized fractions become available for bacteriological and chemical analyses. From such analysis, quantitative and qualitative estimates can be made of the types of bacteria and/or chemicals deposited in various areas of the respiratory tract.