The metabolism of 2, 4-dinitrotoluene (2, 4-DNT), 2, 4-dinitrobenzyl alcohol (2, 4-DNB), 2, 4-dinitrobenzaldehyde(2, 4-DNBAl), 2, 6-DNT, 2, 6-DNB and 2, 6-DNBAl in the microsomal and cytosol fractions prepared from unfortified male Wistar and male Sprague-Dawley (S.D.) rat livers was investigated. Data obtained by high-performance liquid chromatography (HPLC) indicated that the products of dinitrotoluenes (2, 4-DNT and 2, 6-DNT), dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB), and dinitrobenzaldehydes (2, 4-DNBAl and 2, 6-DNBAl) in the microsomal and cytosol preparations containing nicotinamide adenine dinucleotide phosphate (NAD(P)) and reduced NAD(P)(NAD(P)H) were dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB), dinitrobenzaldehydes (2, 4-DNBAl and 2, 6-DNBAl), and dinitrobenzoic acids (2, 4-DNBA and 2, 6-DNBA), and dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB), respectively. From these results, it was concluded that the dinitrobenzaldehydes (2, 4-DNBAl and 2, 6-DNBAl) were intermediates in the oxidations of dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB) to dinitrobenzoic acids (2, 4-DNBA and 2, 6-DNBA), and that the oxidations of dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB) to dinitrobenzaldehydes (2, 4-DNBAl and 2, 6-DNBAl) and the reductions of dinitrobenzaldehydes to dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB) were reversible The result of the consecutive oxidations of 2, 6-DNT in male Wistar rat livers, in the presence of various inhibitors suggests that oxidation of 2, 6-DNT to 2, 6-DNB is done mainly by microsomal cytochrome P-450, oxidation of 2, 6-DNB to 2, 6-DNBAl is mediated by microsomal cytochrome P-450 and nicotinamide adenine dinucleotide (NAD)-dependent alcohol dehydrogenase, oxidation of 2, 6-DNBAl to 2, 6-DNBA may be mediated by NAD-dependent aldehyde oxidase, and reduction of 2, 6-DNBAl to 2, 6-DNB may be mediated by reduced NAD(NADH)-dependent aldehyde reductase. From the comparative investigation of these reaction activities, it was found that : (a) the activity in the 2, 6-DNT oxidation to 2, 6-DNB was higher than that in the 2, 4-DNT oxidation to 2, 4-DNB in both strains, and the activity in Wistar rat was higher than that in S.D. rat; (b) the activities for the reductions of the dinitrobenzaldehydes (2, 4-DNBAl and 2, 6-DNBAl) to dinitrobenzyl alcohols (2, 4-DNB and 2, 6-DNB) were the highest, among the reactions examined, in both strains, and the reduction activity of 2, 4-DNBAl to 2, 4-DNB in Wistar rat was particularly high; (c) the activity for 2, 6-DNB oxidation to 2, 6-DNBAl was higher than that for 2, 4-DNB oxidation to 2, 4-DNBAl in both strains, and the activity in Wistar rat was higher than that in S.D. rat; (d) the activity for 2, 6-DNBAl oxidation to 2, 6-DNBA was much less than that for 2, 4-DNBAl oxidation to 2, 4-DNBA in both strains, and in particular, the activity for oxidation of 2, 6-DNBAl to 2, 6-DNBA in Wistar rat was low. The present results indicate that the metabolism of DNT isomers differs in different strains of rat.