This study deals with the degradation of phenolic compounds in olive oil mill waste; a highly polluting material in olive oil-producing countries because of its abundance and the toxicity of its phenolic compound content. This investigation confirms the ability of an isolated yeast, identified as Trichosporon cutaneum, to degrade phenolic compounds extracted from olive mill waste water (OMW). The yeast was adapted to the OMW by an enrichment culture. The results of this biotransformation were a decrease in the phenolic content and hence a reduction in the phytotoxic effects of the effluent after the yeast treatment. The kinetic growth of the isolated yeast on phenol over a range of concentrations (0.3-3.0 g dm(-3)) was studied. The ability of the strain to assimilate simple monomeric phenols and alkyl phenols, at a concentration of 1 g dm(-3), in a synthetic liquid medium used as the sole carbon source was investigated in a batch culture. The aromatic ring cleavage pathway occurred in the yeast through catechol oxidation. Using various concentrations of ethyl acetate extract from OMW as the sole carbon source, the yeast exhibited growth on the substrate up to 7 g dm(-3) equivalent of phenols. A significant reduction of COD after the treatment of the OMW extract by the yeast isolate was noticed. The removal of phenol and COD exceeded 80% of the original loading after 8 days of treatment, for extracts containing initial COD in the range 19 to 72 g dm(-3). (C) 2004 Society of Chemical Industry.