Two species ofAchromobacterwere isolated from sewage effluent using biphenyl (BP) andp-chlorobiphenyl (pCB) respectively as sole carbon sources.AchromobacterBP grown on biphenyl accumulated a product with an ultraviolet absorption maximum at 257 nm which could not be identified. Washed cell suspensions of both isolates oxidized biphenyl,o-phenylphenol, phenylpyruvate, catechol,p-chlorobiphenyl,m-chlorobiphenyl,o-chlorobiphenyl,o,o′-dichlorobiphenyl, andp,p′-dichlorobiphenyl. Both isolates producedmetacleavage products by fission of the benzene ring. However, spectral characteristics of degradation products from respective substrates were different between the two isolates, indicating divergent degradation pathways. Benzoic andp-chlorobenzoic acids were produced from the degradation of BP andpCB, respectively, byAchromobacter pCB. Chloride was not produced by either isolate during the degradation of all chlorobiphenyls tested including the growth ofAchromobacter pCB onp-chlorobiphenyl.