Starch-processing wastewater was anaerobically treated to produce acetic acid in laboratory-scale, continuously stirred tank reactors. The optimal conditions, in which the maximum acetic acid production occurred, were 0.56 d hydraulic retention time, pH 5.9, and 36.1 degreesC. Acetic acid production at the optimum conditions was 672 +/-20 mg total organic carbon(equivalent) L-1, which indicated a 75% conversion efficiency of influent total organic carbon into acetic acid. A fourth order Runge-Kutta approximation was used to determine the Monod kinetics of the acidogens by using unsteady-state data from continuous unsteady-state experiments at the optimum conditions. The model outputs and experimental data fit together satisfactorily, suggesting that the unsteady-state approach was appropriate for the evaluation of acidogenic biokinetics. These included mu(m), K-s, Y, and k(d), which were evaluated as being 0.13 h(-1), 25 mg total carbohydrate (TC) L-1, 0.38 mg volatile suspended solid mg(-1) TC, and 0.002 h(-1), respectively.