Treatment of landfill leachate has gained increasing attention during recent years, and several commercial RO ieachate treatment plants have been L-,s~lled in, e.g., Germany, the Netherlands and Switzerland. In this investigation the influence on membrane performance when treating new types of landfill leachate was studied. Three different types of landfill leachate were included in this study: leachate from a conventional landfill and two leachates from a new type of landfill. At the new landfill the waste is divided into different categories and deposed in waste cells with separate leachate collecting systems. Leachate from a cell with biodegradable waste and from a cell with special waste, containing mainly ashes, were included in this study. A linear correlation between flux and conductivity was found for leachate both from the conventional landfill and from the biodegradable waste cell. Th~ flux varied, depending on the conductivity of the ieachate, between 48 and 3 I/m2/h. The reduction of pollutants was high. The reduction of the chemical oxygen demam, and NH4-N was more than 98 % for leachate from both ',he conventional landfill and the biodegradable waste, for example. The salt concentration, and thus the osmotic pressure, was very high in the leachate from the cell containing special waste. The flux was thet'efore too low for RO to be a suitable treatment process for this leachate.