In several particle-sizing samplers, the sample extraction nozzle is necessarily closely coupled to the first inertial sizing stage. Devices of this type include small sampling cyclones, right angle impactor precollectors for in-stack impactors, and the first impaction stage of several cascade impactors. In a recent laboratory study of a stack sampling cyclone with various sampling nozzles, significant perturbations were observed in the actual D(sub 50) when some of the nozzles were used. Some nozzles caused the D(sub 50) of the cyclone to be reduced from 10 micrometers to less than 6 micrometers. Several alternate nozzle designs were considered to alleviate this behavior. Simple extension of the nozzle length was sufficient to restore the 10 micrometers sampler D(sub 50), but at the expense of enhanced deposition of the test aerosol particles on the nozzle walls.