Microbial growth and degradation of fluoranthene in amended soil microcosms by the indigenous microbial population and a PAH degrading mixed culture inoculum were characterised. Percentages of fluoranthene disappearance ranged from 14.4% in sterilised uninoculated soil microcosms to 52.1% in unsterilized inoculated microcosms. Inoculated soils had initial microbial counts approximately one order of magnitude higher than the indigenous soil count and exhibited enhanced fluoranthene degradation. Over a nine week incubation period, total viable counts in inoculated non-sterile soil declined to the levels observed for the original indigenous population.