The results of round 116 of the Proficiency Analytical Testing (PAT) program were discussed. The PAT program was a collaborative effort of the American Industrial Hygiene Association and NIOSH scientists designed to assist participating laboratories in improving their analytical performance by evaluating their ability to analyze quality control samples. Each calendar quarter (round), a set of reference samples consisting of a mixture of three of four possible metals, three of 10 possible solvents, amosite or chrysotile, and quartz were sent to participating laboratories. The participating laboratories were evaluated for each analysis by comparing their reported results for each PAT program sample analyzed against an acceptable performance limit established by reference laboratories. Overall laboratory proficiency was rated by evaluating the performance of the participants over the last year, four calendar quarters, and their skill in evaluating each sample. Performance on an individual sample was judged to be proficient if all results were reported and were classified as acceptable over the last two consecutive rounds or 75% of the results reported in the last four rounds were rated as acceptable. Overall laboratory performance was rated as proficient if the results of 67% of the individual samples were considered to be acceptable. A total of 1,427 laboratories were enrolled in the program and 1,319 submitted results for round 116 in which samples containing cadmium, chromium, lead quartz, amosite, 1,1,1-trichloroethane, tetrachloroethylene, and trichloroethylene were analyzed. Approximately 90.1% of the laboratories were rated proficient based on their performance in the last 4 rounds. The authors note that PAT round 117 was sent out on April 1 1994. This round contains chloroform, carbon-tetrachloride, 1,2-dichloroethane, cadmium, lead, zinc, quartz, and chrysotile. The quartz samples have a calcite matrix.