Bacterial strains (190) capable of growth on epsilon-caprolactam as a sole source of carbon and nitrogen were isolated from epsilon-caprolactam industrial sewage. Most of the strains (90%) were found to contain plasmids. Some of the strains (36.8%) assigned provisionally to the genus Pseudomonas contained plasmids controlling epsilon-caprolactam catabolism. The plasmids had a molecular mass from 50 to 300 MDa. Certain plasmids differed in the frequency of conjugation transfer and in the presence of other genetic determinants (resistance against heavy metal ions) and also determined the different character of bacterial growth on epsilon-caprolactam and on its intermediate catabolites.