A mathematical model describing the kinetics of an intermittent-flow, continuous-mix anaerobic reactor (IFCMAR) has been developed from the basic principles of mass balance. The model fakes into consideration the effect of endogenous microbial decay on biogas production and effluent quality. The model has been tested using actual experimental data obtained from a digester operating on dairy manure at various temperatures (25 and 35 degrees C) and retention times (5, 10, 15, 20 and 25 h). It predicted the treatment efficiency, methane yield, and volumetric methane productivity with R-2 ranging from 0.97 to 0.99. Better predictions were observed at the longer hydraulic retention time (HRT) for the lower temperature (25 degrees C) and at the shorter HRT for the higher temperature (35 degrees C) There is a need for more accurate methods for estimating the biodegradability constant of animal waste, as well as the concentration of the active biomass in the reactor.