An isolated perfused lung (IPL) preparation was used to investigate the effects of SO2 (1–2 ppm) on the metabolism of benzo[a]pyrene (BaP), a ubiquitous potent carcinogen that has been associated with the increased incidence of human brochiogenic carcinoma in occupational and urban populations. [14Cj BaP, with and without crude air particulate (CAP), was administered intratracheally to the IPL in conjunction with SO2 or after pretreatment of the whole animal with SO2. Metabolites were isolated from serial blood samples up to 3 h after the administration of /14C/BaP to the IPL. Metabolites were also isolated from lung tissue, washout fluid, macrophage, and trachea and bronchi at the end of the perfusion at 180 min. Patterns of BaP metabolites were determined by thin‐layer and high‐performance liquid chromatography and liquid scintillation counting.