The metabolism of the weakly-carcinogenic hydrocarbon, 9,10-dimethylanthracene (DMA) by rat-liver microsomal preparations has been examined. 9-Hydroxymethyl-10-methylanthracene (9-OHMeMA) and 9,10-dihydroxymethyl-anthracene (9,10-DiOHMeA) were identified as metabolites by comparing their chromatographic and spectral properties with those of the authentic compounds. The trans-1,2-dihydro-1,2-dihydroxy derivative of DMA (DMA 1,2-diol) was the major metabolite formed which was identified by its chromatographic, u.v., n.m.r. and mass spectral properties. The dihydrodiol was also formed in the oxidation of DMA in an ascorbic acid-ferrous sulphate-EDTA system. Two other dihydrodiols that were formed from DMA by metabolism appeared to be the trans-1,2- and 3,4-dihydrodiols of 9-OHMeMA (9-OHMeMA 1,2-diol and 9-OHMeMA 3,4-diol) and the further metabolism of DMA 1,2-diol yielded both of these dihydrodiols. When 9-OHMeMA was further metabolized, two main metabolites were formed; one was identified as 9,10-DiOHMeA and the other appeared to be 9-OHMeMA 3,4-diol. No metabolites were detected when 9,10-DiOHMeA was incubated with rat-liver microsomal fractions.