The Proficiency Analytical Testing (PAT) Program was described, and information was provided on PAT Round 123 and Round 124. The program, a collaborative effort of the Americal Industrial Hygiene Association and NIOSH, evaluated the analytical ability of laboratories, and assisted laboratories in improving performance. Under the program, four sets of samples have been sent out to laboratories quarterly. Sample sets included a mixture of three metals, one to three organic solvents, fibers, and silica (14808607). There were 1,299 laboratories submitting results on Round 123, October 1995. Reference values, performance limits, and number of participants were listed for each sample type for Round 123. For Rounds 120 to 123, 90.0 to 98.9% of laboratories were rated proficient, depending on the contaminant type.