A two-stage, continuous-flow, sequential inoculation bioreactor strategy for the bioremediation of ground water contaminated with creosote and pentachlorophenol (PCP) was evaluated at the bench- and pilot-scale levels. Performance of continually stirred tank reactors (CSTR) using specially-selected microorganisms was assessed according to chemical analyses of system influent, effluent and bioreactor residues, performing a mass balance evaluation, and comparative biological toxicity and teratogenicity measurements. When specially-selected bacteria capable of utilizing (mineralizing) high-molecular-weight polycyclic aromatic hydrocarbons (HMW PAHs) as primary growth substrates were used in pilot-sale bioreactors (120 gal), the concentration of creosote constituents was reduced from ca. 1,000 ppm in the ground water feed (flow rate = 30 GPD) to <7 ppm in the system effluent (removal efficiency of >99%). Notably, the cumulative concentration of 8 HMS PAHs (containing 4 or more fused rings) was reduced from 368 ppm in the ground water fed to 5.2 ppm in the system effluent. Moreover, the toxicity and teratogenicity of the bioreactor effluent was significantly reduced. Biodegradation of PCP was limited (ca. 18%) due in large part to poor inoculation and a high degree of abiotic loss (bioaccumulation and adsorption). In general, field data correlated well with those obtained from bench-scale studies.