General Metals Works PS-1 PUF air samplers and an analytical method based on high resolution gas chromatography - high resolution mass spectrometry (HRGC-HRMS) were evaluated for determination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/PBDFs) and bromo/chloro dibenzo-p-dioxins and dibenzofurans (BCDDs/BCDFs) in ambient air. Dilute solutions of these compounds and C-13(12)-1,2,3,4-TCDD were used to spike the filters of PS-1 air samplers which were then operated 24 hr to sample 350-400 m3 ambient air. After sampling, each quartz-fiber filter and polyurethane foam (PUF) were spiked with C-13(12)-labeled PCDD, PCDF, PBDD, and PBDF internal standards before separate Soxhlet extractions with benzene. The extracts were subjected to an acid/base clean-up procedure followed by clean-up on microcolumns of silica gel, alumina, and carbon and then analyzed by HRGC-HRMS. Results derived from this study indicated the PS-1 ambient air samplers and the analytical procedures were very efficient and that pg/m3 and sub-pg/m3 levels of total PCDDs/PCDFs, PBDDs/PBDFs, BCDDs/BCDFs, and 2,3,7,8-substituted congeners could be accurately measured. Background levels of these compounds in the ambient air were also determined. Total PCDDs, PCDFs, TBDFs, and PeBDFs were detected in a low concentration range of 0.3 to 3.0 pg/m3.