Bacteria (Arthrobacter sp.), isolated from lodgepole pine (Pinus contortus), are capable of utilizing methyl dehydroabietate as the sole source of carbon. Degradation products of methyl dehydroabietate have been obtained by manually extracting the cell-free supernatant solution of a liquid growth medium with methylene chloride. Gas chromatography (G. L. C.) was used for separation of the neutral products. The acid products were converted to their methyl esters diazomethane and then separated by gas chromatography. Structures have been proposed for two G. L. C. fractions (V, II) on the basis of infrared (I.R.) and mass spectral (M. S.) data. The molecular weight of V is 328, corresponding to the introduction of one oxygen atom into methyl dehydroabietate, (M. W. 314) and loss of two protons. Infrared peaks at 5.73µ and 5.77µ. , and the absence of a large P-l mass spectral peak (P-1 is due, to loss of the aldehydic hydrogen) indicate that the material is a keto- ester. A comparison of the fragmentation pattern of V and the fragmentation pattern of methyl dehydroabietate indicates that the ketone carbonyl group is in ring A of methyl dehydroabietate and is β to the ester carbonyl group. The molecular weight of II is 260. Present in its infrared spectrum are peaks associated with a non-conjugated methyl ester (5.73µC=O; 8. 30µ, 8. 39µ, 8. 54µ, C-O) and the aromatic ring (6. 21µ, 6. 67µ, and 6.89µ) with isopropyl substitution (7. 30µ, 7.37µ). Significant mass spectral peaks at (1) 233 (P-27), (2) 201 (P-59), (3)200 (P-60), (4) 159 (P-101) and (5) 129 (P-131) are consistent with structure II.