A combination of modified Fenton and biological treatment was used to remove polycyclic aromatic hydrocarbons (PAHs) from creosote oil-contaminated soil. After modified Fenton reaction the toxicity of column leachate and soil to Vibrio fischeri increased. The number of intact bacterial cells and utilisation of PAHs in PAH utilisation microplate assay decreased after modified Fenton reaction. However, bacteria in chemically treated soil utilised PAHs without addition of other carbon sources. The activity of extracellular esterases increased during incubation of modified Fenton-treated soil. PAH removal in combined chemical oxidation and incubation (43-59%) was higher than in incubation alone (22-30%). Residual H2O2 in soil allowed chemical oxidation of PAHs during incubation. (c) 2006 Society of Chemical Industry.