Pseudomonas putida 39/D oxidized p-xylene to cis-3,6-dimethyl-3,5-cyclohexadiene-1,2-diol (cis-p-xylene dihydrodiol). The latter compound was isolated in crystalline form and its physical properties were determined. The cis configuration of the hydroxyl groups in the oxidation product was inferred from its ability to form an isopropylidene derivative with 2,2-dimethoxypropane. Acid treatment of cis-p-xylene dihydrodiol resulted in the formation of 2,5-dimethylphenol. A partially purified preparation of cis-toluene dihydrodiol dehydrogenase oxidized cis-p-xylene dihydrodiol to 1,2-dihydroxy-3,6-dimethylbenzene (3,6-dimethylpyrocatechol). P. putida 39/D oxidized m-xylene to a compound whose spectral and chromatographic characteristics were consistent with the structure 3,5-dimethyl-3,5-cyclohexadiene-1,2-diol. This product was very unstable, and all attempts to isolate it led to the formation of 2,4-dimethylphenol.