The background and current status of the proficiency analytical testing (PAT) program were discussed. PAT was designed to assist laboratories in improving their ability to analyze samples of occupational and environmental relevance. The program provided quality control reference samples to more than 1,300 laboratories in 17 countries. Each calendar quarter (round), reference samples 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 manmade fibers; and one to three of the solvents benzene (71432), chloroform (67663), 1,2-dichloroethane (107062), methanol (67561), p- dioxane (123911), tetrachloroethylene (127184), toluene (108883), 1,1,1-trichloroethane (71556), trichloroethylene (79016), o-xylene (95476), methyl-ethyl-ketone (78933), and methyl-isobutyl-ketone (108101) are mailed to the participating laboratories. The participants are evaluated for each analysis by comparing their reported results against acceptable values established for each sample. PAT round 128 was sent out in January 1997 to 1,324 participating laboratories. Round 128 was the first round in which methyl-isobutyl-ketone and methyl-ethyl-ketone were used as solvent analytes, and the second practice round for passive monitors. There were 1,217 laboratories which submitted results; 332 of 356 laboratories were rated proficient for the metals analysis, 77 of 78 were rated proficient for the silica analysis, 989 of 1,031 were rated proficient for the fibers analysis, and 288 of 320 were rated proficient for the solvents analysis. PAT round 129 was sent out in April 1997. The solvents in this round were 1,2-dichloroethane, tetrachloroethylene, and trichloroethylene, the metals were cadmium, lead, and zinc, the silica sample had a calcite background, and the fiber sample included chrysotile with one manmade fiber.