Five pseudomonads and two Burkholderia spp. capable of utilizing naphthalene or phenanthrene as a sole source of carbon and energy were isolated from oil-contaminated soils through enrichment cultures. All the strains studied contained large plasmids. In six strains, they were involved in biodegradation of specific substrates. The major intermediates of phenanthrene metabolism accumulated in the culture liquids were 1-hydroxy-2-naphthoate and 2-hydroxy-1-naphthoate. The strains studied differed in the accumulation pattern of these intermediates. 2-Naphthol, an oxidation product of 2-hydroxy-1-naphthoate, exerted a toxic effect on microorganisms. The phenanthrene-degrading activity of Pseudomonas strains depended on their ability to utilize 1-hydroxy-2 naphthoate. In the Pseudomonas strains under study, phenanthrene metabolism involved the enzymes of naphthalene degradation.