In this study a new method is developed to determine a flow duration curve (FDC) for a process in which stream flow is defined as a product of two variables, representing the periodic and the stochastic components, respectively. The cumulative frequency distribution is obtained via integration procedures and also given as an algorithm for discrete variables. Hence the exceedance probability for any given flow value can be calculated. The method is applied to daily flow data from many sites and it is found that the FDCs based on this method compare well with the observed FDC. Furthermore the FDCs developed in this method compare well with other methods in the recent literature. It was found that non-dimensional flow duration curves in Turkey can be characterized by three, or sometimes just two, parameters. Values of these parameters have been estimated at many sites enabling a FDC to be constructed at neighbouring sites for which only the drainage basin area is known. Copyright (C) 2000 John Wiley & Sons, Ltd.