In this study we monitored for 920 days the sulfate (SO42-), chloride (Cl-), chemical oxygen demand (COD) and biological oxygen demand (BOD) parameters in leachate produced in two large-scale test cells at the Odayeri Sanitary Landfill, Istanbul, Turkey. We present a mathematical model of these parameter concentrations in leachates of two test cells with one being the control (C I) and the other (C2) leachate recirculation. The relationship between these parameters and refuse age is simulated by a mathematical formula. The unknown constants of the simulation formula are solved by the least squares method, which minimizes the squared total of deviation from the model of the actual data using a MATLAB (R) computer program. A good fit was obtained between the measured data and model simulations. COD concentrations in leachate from C1 and C2 rapidly attained their maximum values of 75 and 70 g/l, respectively, after I month of landfilling. BOD to COD ratios are around 0.8 for both test cells during the acidogenic phase; this ratio then decreased to 0.06. A sharp decrease in the concentration of Cl- from 14 to 15 g/l was observed after approximately 2 months of operation, followed by a slow decrease. SO42- concentrations rapidly reached a maximum value of 2000 mg/l within 45 days; development of anaerobic conditions caused a sharp decrease to around 75 mg/l for C2 and 450 mg/l for C1 after 5 months of operation. The results showed that there appeared to be little improvement in leachate quality by leachate recirculation in terms of COD and BOD values, however, it is determined that the pollution loads more rapidly reached minimum values within the C2 test cell. (c) 2005 Elsevier B.V. All rights reserved.