Winery wastewaters, being seasonal and experiencing substantial flow variations, are difficult to treat by conventional biological processes. This work proposes the photo-Fenton reaction in homogeneous phase as an alternative for their purification. Experimental design methodology has been used in order to study the main variables affecting the oxidation process as well as their most relevant interactions. Under energetic conditions the photo-Fenton treatment reached purification levels of up to 95% (measured as total organic carbon). The most influential factors behind organic matter removal are the Fe3(+) and H2O2 dosage. The influence of the initial organic matter concentration and the reaction time is almost negligible for the confidence level selected (90%) in the results analysis. (c) 2006 Elsevier B.V. All rights reserved.