The background and current status of the Environmental Lead Proficiency Analytical Testing (ELPAT) Program were reviewed. The ELPAT Program was administered by the American Industrial Hygiene Association, NIOSH, and the United States Environmental Protection Agency (EPA). Proficiency test samples, consisting of real world paint chips, dust wipes, and soils, were sent on a quarterly basis to participating laboratories. The analytical results of the participating laboratories were compared to those of the selected reference laboratories. The acceptable performance limits were +/-3 standard deviations of the statistically treated reference laboratory data. Laboratories were rated based on performance in four rounds of the ELPAT program. ELPAT Round 20 was sent to 371 laboratories in October 1997. A total of 350 laboratories submitted results. The relative standard deviations of the reference laboratories ranged from 6.3 to 7.5% for paint chips, 5.4 to 15.0% for soils, and 6.1 to 7.7% for dust wipes. The proportion of outliers in the participating laboratories ranged from 4.9 to 6.7% for paint chips, 5.0 to 11.7% for soils, and 5.1 to 7.3% for dust wipes. For one paint chip sample and two dust wipe samples, flame atomic absorption spectroscopy had a positive bias over inductively coupled plasma atomic emission spectroscopy (ICP/AES). Anodic stripping voltammetry also had a positive bias over ICP/AES in one paint chip sample. Although biases due to instrumental technique were often observed in the ELPAT Program, no biases due to sample preparation technique were found thus far. The authors conclude that successful performance in a proficiency testing program such as the ELPAT Program is required for accreditation by the EPA's National Lead Laboratory Accreditation Program.