A selected microbial consortium(SMC), using pentachlorophenol(PCP) as a sole carbon source was developed. For systems of nonpretreated and fungally or chemically pretreated PCP, the resulting growth rates were determined and compared. Pretreatment was accomplished using the white-rot fungus Phanerochaete chrysosporium or Fenton`s Reagent. Growth rate kinetics were described by the Haldane Model. Haldane constants were used as the basis of comparison. Results indicate that both fungal and chemical pretreatment effected a significant decrease in toxicity when compared with nonpretreated systems. In addition, fungal pretreatment decreased PCP toxicity to a greater extent than did chemical pretreatment at the chemical doses investigated for this study. At PCP concentrations above 47㎎/ℓ, for the fungal pretreatment system, at PCP concentration above 29㎎/ℓ, for the chemical pretreatment system, toxicity gradually increased. Possible mechanisms for these results are explained using cometabolism.