Olive oil extraction produces large amounts of waste water, known as olive mill waste water (OMWW). This has a high chemical oxygen demand and contains high levels of phenolic compounds, and is therefore a cause of environmental pollution. The major aim of this study was to investigate the use of OMWW as a moisture source for mushroom cultivation. Pleurotus sajor-caju and P. cormicopiae var. citrinopileatus were grown on wheat straw substrate moistened with different OMWW:tap water mixtures. In terms of mycelial growth, time for initiation of primordia and crop yield, substrate moistened with mixtures containing 25% and 50% OMWW was found to be suitable for cultivation of both organisms as compared with control medium which contains tap water as a moisturiser. However, moistening with a mixture containing 75% OMWW or with OMWW alone was not compatible with cultivation of these organisms. (C) 2003 Elsevier Ltd. All rights reserved.