When inoculated at high cell densities, three strains of Pseudomonas cepaciu degraded the polycyclic aromatic hydrocarbons (PAHs) benzo[a]pyrene, dibenz [u,h]anthracene and coronene as sole carbon and energy sources. After 63 days incubation, there was a 20 to 30% decrease in the concentration of benzo [u]pyrene and dibenz [u,h]anthracene and a 65 to 70% decrease in coronene concentration. The three strains were also able to degrade all the PAHs simultaneously in a PAH substrate mixture containing three-, four-, five-and sevenbenzene ring compounds. Furthermore, improved degradation of the five-and seven-ring PAHs was observed when low molecular weight PAHs were present.