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 1,400 participating laboratories in 18 countries. Each calendar quarter (round) reference samples consisting of mixtures of three of the metals cadmium, chromium, lead, or zinc, silica, either amosite, chrysotile, or manmade fibers, and one to three of the solvents benzene, chloroform, 1,2-dichloroethane, methanol, p- dioxane, tetrachloroethylene, toluene, 1,1,1-trichloroethane, trichloroethylene, or o-xylene were mailed to the participating laboratories. The participants were evaluated for each analysis by comparing their reported results against acceptable values established for each sample. A participating laboratory was 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 as acceptable. PAT round 122 was sent out in July 1995 to 1,419 participating laboratories. A total of 1,306 laboratories submitted results. Combining the results reported by the laboratories in round 122 with those reported previously in rounds 119, 120, and 121 indicated that 92.9% of the laboratories were rated proficient in the metals analysis, 97.7% in the silica analysis, 94.8% in the asbestos analysis, and 88.0% were rated proficient in the solvents analysis. PAT round 123 was mailed out in September 1995. The solvents in this round included chloroform, 1,2-dichloroethane, and tetrachloroethylene. The metals included cadmium, lead, and zinc. Silica was in a talc and coal mine dust matrix. The fiber samples included chrysotile and glass fibers.