Air samples are collected by drawing workplace air, using personal sampling pumps, through 37-mm mixed cellulose ester (MCE) filters mounted in polystyrene cassettes. Samples are prepared for XRF analyses by transferring each filter, along with the support pad, to a special air filter sample holder, specifically designed for a Niton XRF analyzer. Three separate 60-second readings are taken with the analyzer (three different areas of the filter are measured: middle, top and bottom) for each filter sample. From these three readings, the analyzer calculates the total micrograms of Pb per sample filter. After making a blank correction, the concentration of Pb in air, found on the filter, is determined by dividing the micrograms found by the cubic meters of air sampled. The material that is invariably deposited on the insides of the cassette tops during sampling must be determined and added to the amount found on the corresponding filter to determine the final concentration of Pb in the sampled air. The deposited material is physically removed with a Ghost Wipe. The Ghost Wipes may also be analyzed for Pb by portable XRF using OSHA method OSS11 or they may be submitted to the laboratory for analysis.