In order to evaluate the possibility of reusing Olive oil Mill Wastewater (OMW) for irrigation in the area of Marrakech Morocco, wastewaters from three olive oil extraction processes (traditional, semi-modern and continuous) were compared. All non-diluted samples of OMW completely blocked the germination of Ordeum vulgare seeds. Germination of all seeds was obtained for a dilution of 1/16 of OMW but only for continuous process samples. The OMW from traditional units seemed to be the most toxic as confirmed by the MetPAD(TM) assay, heavy metal concentration, total phenols and other organic parameters. This higher toxicity is probably related to the traditional process OMW low water content. Nevertheless, despite lower aerobic bacteria counts for the traditional and semi-modem OMW, yeast counts were close for all OMW samples with yeasts showing higher concentrations than fungi and bacteria. Furthermore, among 105 yeast strains, isolated from OMW, around 20 were able to grow on all three OMW. (C) 2005 Elsevier Ltd. All rights reserved.