A model was developed for the anaerobic digestion of a glucose-based medium in an innovative high-rate reactor, the periodic anaerobic baffled reactor (PABR). The model considers each PABR compartment as two variable volume interacting sections, of constant total volume, one with high solids and one with low solids concentration, with the gas and liquid flows influencing the material flows between the two sections. For the simulation of glucose degradation, the biomass was divided into. acidogenic, acetogenic and methanogenic groups of microorganisms. The kinetic part of the model accounted for possible inhibition of acidogenesis, acetogenesis and methanogenesis by volatile fatty acids. The model succeeded in predicting the reactor performance upon step increases in the organic loading rate.