The background and current status of the proficiency analytical testing (PAT) program were presented. 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 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 acceptable. PAT round 123 was sent out in October 1995 to 1,407 participating laboratories. A total of 1,299 laboratories submitted results. Combining results reported by laboratories participating in round 123 with those reported previously in rounds 120, 121, and 122 indicated that 92.3% of the laboratories were rated proficient in the metals analysis, 98.9% in the silica analysis, 96.0% in the fibers analysis, and 90.0% were rated proficient in the solvents analysis. Round 124 was sent out in January 1996. The solvents in this round were 1,2-dichloroethane, tetrachloroethylene, and trichloroethylene. The metals were cadmium, chromium, and lead. Silica was presented in a coal mine dust matrix and the fiber sample was amosite.