The background and current status of the proficiency analytical testing (PAT) program were discussed. PAT was a collaborative effort of the American Industrial Hygiene Association and NIOSH designed to assist participating laboratories in improving their ability to analyze samples of occupational and environmental relevance. The program provided quality control reference samples to more than 1,800 participating laboratories in 18 countries. Each calendar quarter (round) reference samples were mailed to the participating laboratories, consisting of mixtures of three of the metals cadmium (7440439), chromium (7440439), lead (7439921), or zinc (7440666); silica (14808607); either amosite (12172735), chrysotile (12001295), or man made fibers; and one to three solvents. The participants were evaluated for each analysis by comparing their reported results against acceptable values established for each sample. PAT round 126 was sent out in July 1996 to 1,324 participating laboratories. There were 1,218 laboratories which submitted results. Altogether, 332 of 361 laboratories were rated proficient for the metals analysis, 81 of 82 were rated proficient for the silica analysis, 986 of 1,030 were rated proficient for the fiber analysis, and 300 of 332 were rated proficient for the solvents analysis. PAT round 127 was sent out in October 1996. The organic solvents in this round were chloroform (67663), 1,2-dichloroethane (107062), and tetrachloroethylene (127184), the metals were cadmium, lead, and zinc, the silica sample had a talc and coal dust background, and the fiber sample included chrysotile with one man made fiber.