By applying some biokinetic models to data obtained from experimental studies carried out on a laboratory scale anaerobic hybrid model reactor, determination of some kinetic constants of the reactor was aimed. Treatment efficiencies of the model reactor were investigated at different hydraulic retention times (0.5, 1, and 2 days) and organic loading rates (1-10 kgCOD/m(3)*d). Most suitable models were determined and kinetic parameters were calculated depending on the operational conditions. As a result of the calculations, second-order model and a Stover-Kincannon model were found to be the most appropriate models for the hybrid reactor. The second order substrate removal rate constant (k(2(S))) was found as 2.32, 2.57, and 10.81 per day for sludge bed region, fixed bed region, and overall reactor, respectively. Applying the modified Stover-Kincannon model to the fixed bed region of the reactor, the maximum removal rate constant (U-max) and saturation value constant (K-B) were found to be 83.3 and 186.23 g 1 per day, respectively. (C) 2002 Elsevier Science Ltd. All rights reserved.