The background and status of the Proficiency Analytical Testing (PAT) program were reviewed. Through the program, occupational health and testing laboratories were given the opportunity to evaluate their analytical abilities and improve their laboratory performance. The comparison of analytical results of contaminant samples collected from the member laboratories with data obtained from reference laboratories, and the rating of the laboratories based on PAT performance criteria, were described. Current sets of samples in the programs included heavy metals, silica (14808607), asbestos (1332214), and organic solvents. Information of the reference values, performance limits, and participants for each sample type from PAT Round 118 and PAT Proficiency Ratings based on Rounds 115 to 118 were given in tables. Of the 1384 laboratories evaluated in the PAT program, 92.8% were assessed as overall proficient. PAT Round 119, October 1994, was discussed. Sample sets in the round included carbon-tetrachloride (56235), 1,2- dichloroethane (107062), and trichloroethylene (79016) for the organic solvents; metals included cadmium (7440439), lead (7439921), and zinc (7440666); talc (14807966) and coal mine dust for silica; and chrysotile (12001295) for asbestos. A new organic solvent analyte to be included in the PAT program for 1995 may be methanol (67561) on silica-gel tubes.