Olive mill wastewater (OMW) is an effluent of the olive oil extraction process. The large volumes involved, along with the high phenolic content and chemical oxygen demand, cause major environmental problems. The presence of phenolics limits the effectiveness of aerobic or anaerobic treatment of this wastewater. In most of the studies performed on OMW, the concentration of phenolics is reduced by diluting the OMW prior to biological treatment, which leads to an increase in waste volume. Therefore, the aim of this work was to investigate the possibility of reducing the phenolic content without dilution and without any addition of nutrients or pretreatment by using the white-rot fungi Trametes versicolor FPRL 28A INI. Through an adaptation process, the fungus was able to remove 78% of total phenolics in shake flask experiments and 39% in static culture using undiluted OMW medium. In continuously stirred tank reactor (CSTR) conditions, 70% of total phenolics removal was achieved. Analysis with GC-MS showed that all simple phenolics disappeared from the medium after the 8th day of cultivation at an 0.25 vvm aeration rate. The maximum activities of phenol degrading enzymes laccase and manganese peroxidase (MnP) obtained under these conditions were 762.14 +/- 42.11 and 97.80 +/- 8.11 U l(-1) respectively. (c) 2008 Elsevier Ltd. All rights reserved.