Benzo (a) pyrene, added to the nutrient solutions of cell suspension cultures of Chenopodium rubrum, was metabolized to oxygenated derivatives. With increasing time of incubation decreasing amounts of the added 14C-radioactivity could be extracted with 70% methanol or be isolated as benzo (a) pyrene. The amount of metabolites formed increased with increasing time of incubation. After 48 hours most of the radioactivity was found in the extracted residue. These observations and some other indications give reason to believe that some of the metabolites are linked to proteins or nucleic acids.