A Pseudomonas stutzeri strain capable of growing on o-xylene was isolated from enrichment cultures. The organism grew on 2,3- and 3,4-dimethylphenol but not on 2-methylbenzyl alcohol, o-tolualdehyde, or o-toluate. P. stutzeri was not able to utilize m-xylene, p-xylene, or 1,2,4-trimethylbenzene, but growth was observed in the presence of the corresponding alcohols and acids. From the Pseudomonas cultures supplied with o-xylene, 2,3-dimethylphenol was isolated and identified. When resting P. stutzeri cells were incubated with 2,3-dimethylphenol, the reaction mixture turned greenish yellow and showed spectral properties identical to those of the 3,4-dimethylcatechol meta ring fission product. Catechol 2,3-oxygenase was induced by growth on o-xylene or on 2,3- or 3,4-dimethylphenol. The suggested hypothesis is that the first metabolic steps of growth on o-xylene involve the direct oxygenation of the aromatic nucleus, followed by meta pathway reactions.