A fundamental study of the collection efficiency resulting from inertial deposition of particles onto large pore Nuclepore filters has been conducted. The theoretical procedure involved the solution of the Navier-Stokes equations for steady flow through a representative filter pore. Stokes' drag forces were applied to a particle in the flow field and used to determine its trajectory. The critical trajectory for deposition was found, and the collection efficiency was determined. The solutions were obtained numerically. The study was restricted to continuum flow and assumed negligible particle diffusion. The theory was used to investigate the influence of pore Reynolds number, particle density, filter thickness, and filter porosity upon the collection efficiency. Experimental collection efficiencies were obtained for laboratory generated particles. The filters were analyzed using optical fluorescence techniques. The experimental results obtained for a liquid aerosol are in good agreement with the theory and are viewed as validation of the impaction theory developed. The experimental results obtained for a solid aerosol fall well below the theoretical predictions and are viewed as an indication of particle bounce for a non-sticky aerosol.