Using the conventional enrichment technique various bacteria were isolated capable of degrading simple aromatic hydrocarbons such as naphthalene, phenanthrene, and anthracene. One isolate had the capacity to co-oxidize fluorene, fluoranthene, and pyrene; the higher condensed aromatics, however, were not attacked. Ecological studies in soil percolators revealed that a variety of polycyclic aromatic hydrocarbons including benzo(a)-pyrene and benzo(a)anthracene were degraded by microbial activities.