An experimental study of the filtration performance of several commercially available, NIOSH-approved, disposable respirators was conducted using monodisperse DOP and NaCl particles with diameters in the 0.035 to 4 pm range. The aerosol penetration through the respirators were measured at flow rates of 16,28 and 48 L/m using a condensation nucleus counter, an aerodynamic particle sizer, and a laser optical particle counter for purposes of comparison. The results obtained by these instruments were found to be in good agreement with each