Pure cultures of anaerobic intestinal bacteria and mixed fecal microflora from human, rat, mouse, and pig were screened for the ability to metabolize 7‐nitrobenz[a]anthracene (7‐NO2BA). Based on analysis by high‐performance liquid chromatography (HPLC) and by ultraviolet (UV), mass, and nuclear magnetic resonance (NMR) spectral techniques, the compounds were identified as 7‐aminobenz[a]anthracene (7‐NH2BA) and benz[a]anthracene 7, 12‐dione (dione). Identification of 7‐NH2BA as a metabolite of 7‐NO2BA indicates that the anaerobic intestinal bacteria are capable of reducing 7‐NO2BA to potentially bioactive intermediates. The reductive capacities of the mixed intestinal microflora were generally greater than those of pure cultures. Thus, metabolism of 7‐NO2BA in the intestinal tract may 6e underestimated if pure cultures are used as the sole method for evaluating the potential hazard.