A research protocol for the evaluation of the workplace protection factor provided by two models of powered air purifying respirators is reviewed. Laboratory evaluation of two models (including filter penetration tests) is described. Field tests of performance on workers involve simultaneous sampling of front and rear outside and inside face piece lead (7439921) concentrations. Lead analysis using atomic absorption spectroscopy and a graphite furnace technique is recommended. Filter handling, wearing, and maintenance of the respirators are described. Preshift quantitative fit testing is discussed. The effect of worker head movements on fit and the relation to the respirator protection factor are examined. Recommendations are made for worker instructions and monitoring. Testing of respirators on manikin heads is also described. Aerosol characterization to determine the effect of particle size distribution on respirator performance is considered. The authors conclude that the described research protocol provides for proper respirator fitting, use, wear, maintenance, worker supervision, and sampling, all of which are problems commonly associated with data acquisition when field testing respirators. Based on successful implementation of this protocol, the observed workplace performance of these respirators should be indicative of their best performance capability under workplace conditions experienced during the study.