Bench-scale biotreatability studies were performed to determine the most effective of two bioremediation application strategies to ameliorate creosote- and pentachlorophenol (PCP)-contaminated soils present at the American Creosote Works Superfund site, Pensacola, Florida: solid-phase bioremediation or slurry-phase bioremediation. When indigenous microorganisms were employed as biocatalysts, solid-phase bioremediation was slow and ineffective (8-12 weeks required to biodegrade >50% of resident organics). Biodegradation was limited to lower-molecular-weight constituents rather than the more hazardous, higher-molecular-weight (HMW) compounds; PCP and HMW polycyclic aromatic hydrocarbons (PAHs) containing 4 or more fused rings resisted biological attach. Moreover, supplementation with aqueous solution of inorganic nutrients had little effect on the overall effectiveness of the treatment strategy. Alternatively, slurry-phase bioremediation was much more effective: >50% of targeted organics were biodegraded in 14 days. Again, however, more persistent contaminants, such as PCP and HMW PAHs, were not extensively degraded when subjected to the action of indigenous microorganisms.