A fluidized-bed reactor, with sand as the carrier and ethanol as the carbon and electron source, was investigated for the biological denitrification of ground water. The paper concentrates on the reactor’s kinetics, with special emphasis on nitrite as the intermediate product. Intrinsic zero-order kinetic parameters for both nitrate and nitrite were determined by batch and continuous experiments. Values for the maximum specific nitrate and nitrite removal rates of 11 g and 6 g NO3- (g volatile suspended solids)(-1) day(-1), respectively, were obtained. These values were used to interpret nitrate and nitrite concentration profiles in an experimental fluidized-bed reactor operating at different conditions of hydraulic loading and retention time.