The background and current status of the proficiency analytical testing (PAT) program were discussed. PAT is 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 provides quality control reference samples to more than 1,800 participating laboratories in 18 countries. Each calendar quarter (round) reference samples consisting of mixtures of cadmium (7440439), chromium (7440473), lead (7439921), or zinc (7440666), silica (14808607), either amosite (12172735), chrysotile (12001295), or man made 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), or o-xylene (95476) 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. A participating laboratory is rated as proficient if all results were reported and all were classified as acceptable during the last two consecutive rounds or if at least 75% of the results reported in the last four consecutive rounds were classified acceptable. PAT round 125 was sent out in April 1996 to 1,330 participating laboratories. A total of 1,201 laboratories submitted results. Of these, 95.0% were rated proficient for the metals analysis, 98.8% proficient for the silica analysis, 95.6% proficient for the fiber analysis, and 89.0% were rated proficient for the organic solvents analysis. PAT round 126 was sent out in July 1996. The organic solvents in this round were benzene, o-xylene, and toluene, the metals were cadmium, chromium, and lead, the silica sample had a talc background, and the asbestos sample was amosite.