A sampling system was designed for the collection of contaminant particles within the face piece of a powered air purifying respirator. The system consisted of a stainless steel inlet probe secured to the face piece of the respirator, a standard filter cassette, and a personal sampling pump. Design and performance of two inlets were evaluated. One inlet was a cylinder 3.5 millimeters (mm) in diameter; the second was funnel shaped and 8.1mm in diameter at the widest part of the funnel. These inlets were attached to a powered air purifying respirators mounted on a manikin head connected to a breathing machine. Aerosol particles of 2.0, 5.0, 8.0, and 10.0 micrometers (microm) were injected into the flexible hose between the powered blower unit and the face piece of the respirator. Particles used were oleic-acid droplets with a small amount of uranine dye added to allow measurement of the droplet mass with a fluorometric technique. The funnel inlet was also tested at airflow rates of 1, 2, or 4 liters per minute. For the cylindrical inlet, the penetration decreased from 93.4 percent for 2microm particles to 32 percent for 10microm particles. With the funnel shaped inlet, the penetration was 100 percent for the small particles. When the airflow increased, penetration of the largest particles dropped to 91.9 percent. The absence of deposition of particles on the inlet surfaces was taken as evidence that 100 percent sampling efficiency was achieved; this was true of the funnel inlet for 2.0 and 5.0microm particles. The authors conclude that a properly designed inlet system can have high efficiency for aerosol sampling in the face piece of a powered air purifying respirator.