Whole-body low-temperature radioluminography of (3)H-2,6-xylidine in rats indicates that the nonmetabolized substance, which is a volatile and fat-soluble compound, is distributed throughout the body and accumulates in adipose tissues, e.g., in the abdominal and subcutaneous regions. Whole-body autoradiography with freeze-dried or solvent-extracted tissue sections as well as microautoradiography, which were used to trace tissues in the rats accumulating 2,6-xylidine metabolites, showed presence of tissue-bound 2,6-xylidine metabolites in the nasal olfactory mucosa and the mucosa of the upper alimentary and respiratory tracts. These tissues were found to have an in vitro capacity to bioactivate 2,6-xylidine. Our data indicate that 2,6-xylidine in vivo undergoes an in situ bioactivation in these extrahepatic tissues. Our results showed that the nasal olfactory mucosa had a much higher capacity than the other examined tissues to bioactivate 2,6-xylidine. Thus, the carcinogenic effect of 2,6-xylidine toward the nasal mucosa in rats is correlated with a high capacity of this tissue to bioactivate the compound.