The principal aim of this research was to evaluate the ability of different Yarrowia lipolytica strains, having different origin, to grow in olive mill wastewater (OMW) and reduce its COD level. All the strains were able to grow in undiluted OMW; the comparison between the data obtained in a semi-synthetic medium and in OMW suggests that lipases with different specificity can be produced in relation to the medium composition. Under the adopted conditions, the reduction of the OMW COD values varied from 1.47% and 41.22%, of the initial value. Some strains determined a significant reduction of polyphenol content, while other ones caused its apparent increase. Moreover, some Y. lipolytica strains, isolated from chilled foods, produced the highest citric acid concentrations. These results evidenced that some Y. lipolytica strains are good candidates for the reduction of the pollution potential of OMW and for the production of enzymes and metabolites such as lipase and citric acid. (C) 2004 Published by Elsevier Ltd.