The results of Round 121 of The Proficiency Analytical Testing (PAT) Program were presented. The PAT program, conducted by the American Industrial Hygiene Association in collaboration with the Centers for Disease Control and Prevention and NIOSH has been an ongoing process assessing the performance of occupational health and environmental laboratories in 18 countries by evaluating the results of sample analyses conducted by the laboratories on referent materials. Changes in the PAT program that were introduced in Round 121 were described. These included the use of a new format for individual laboratory reports as well as changes in the way laboratories were evaluated by the PAT program. Individual laboratory proficiency ratings were replaced with a rating for each type of sample analyzed. Between 1.0% and 9.2% of laboratories were rated nonproficient for PAT Rounds 118 through 121 which involved analyses of metals, silicas, asbestos (1332214), and organic solvents. A description of PAT Round 122, sent to participating laboratories in June 1995, was presented.