The penetration characteristics of a horizontal plate elutriator and of a 10-mm nylon cyclone were evaluated. The test aerosols were polydisperse coal dust particles ranging from less than 0.3 to 15 micrometers in diameter. Particle densities ranged from 1.3 to 1.4 Grams per cubic centimeter. Equivalent stokes diameters were measured using coulter counter analytical techniques. Experimental results indicate that the penetration characteristics of the horizontal plate elutriator closely approximate the sampling efficiency curve defining the respirable fraction of the dust cloud recommended and adopted by the johannesburg pneumoconiosis conference in 1959. Penetration characteristics of the 10-mm cyclone were evaluated at flow rates of 1.4, 1.5, 2.0, 2.5, and 2.8 Liters of air per minute. The data indicate that the penetration curve obtained at 2.0 Liters per minute most closely approximates the sampling efficiency curve for respirable dust recommended at a meeting sponsored by the U.S. Atomic Energy Commission in 1961.