Background information and the current status of the Proficiency Analytical Testing (PAT) Program, a collaborative effort of the American Industrial Hygiene Association (AIHA) and researchers at the National Institute for Occupational Safety and Health (NIOSH) were provided. It was noted that each calendar quarter samples are mailed to participating laboratories and the data are analyzed to evaluate laboratory performance on a series of analyses. A combination of three metals and three organic solvents were rotated for each round. Laboratories were evaluated for each analysis by comparing their reported results against an acceptable performance limit for each PAT Program sample the laboratory analyzes. Laboratories were rated based on performance in the PAT Program over the last year as well as on individual contaminant performance and overall performance. In PAT Round 103, October of 1990, chromium (7440473) was included for the first time as chromium(III)-nitrate- nonahydrate (7789028). The results reported by the reference laboratories had a relative standard deviation range of 5.7% to 6.3%. A total of 1578 laboratories was enrolled in the PAT Program with 1459 laboratories submitting results on Round 103. PAT Round 104 was sent on January 2, 1991 containing 1,1,1-trichloroethane (71556), tetrachloroethylene (127184), and trichloroethylene (79016) as the solvents and cadmium (7440439), lead (7439921), and zinc (7440666) as the metals. Also included was silica (14808607) with a coal mine dust as the background and a sample of amosite (12172735) asbestos.