A γ-hexachlorocyclohexane (HCH)-degrading bacterium, Sphingomonas sp. MM-1, was isolated from soil contaminated with HCH isomers. Cultivation of MM-1 in the presence of γ-HCH led to the detection of five γ-HCH metabolites, γ-pentachlorocyclohexene, 2,5-dichloro-2,5-cyclohexadiene-1,4-diol, 2,5-dichlorohydroquinone, 1,2,4-trichlorobenzene, and 2,5-dichlorophenol, strongly suggesting that MM-1 has the lin genes for γ-HCH degradation originally identified in the well-studied γ-HCH-degrading strain Sphingobium japonicum UT26. Southern blot, PCR amplification, and sequencing analyses indicated that MM-1 has seven lin genes for the conversion of γ-HCH to β-ketoadipate (six structural genes, linA to linF, and one regulatory gene, linR). MM-1 carried four plasmids, of 200, 50, 40, and 30 kb. Southern blot analysis revealed that all seven lin genes were dispersed across three of the four plasmids, and that IS6100, often found close to the lin genes, was present on all four plasmids.