SummaryBy annual measurements of population size, fertility and recruitment on a buffalo population in the Serengeti it has been possible to construct a model that predicts the equilibrium level of this population. This model also suggests that the population is increasing towards an equilibrium position, and that adult mortality is the only regulating mortality needed to achieve this equilibrium. Juvenile mortality shows large fluctuations from year to year and potentially is the most important mortality in causing fluctuations in population size.By extrapolating the model population backwards in time it is possible to observe that the real population has experienced a higher mortality or lower fertility in the past, and there is evidence from the rinderpest disease at that time which suggests that this could have been a possible cause. The models can be adapted to incorporate changing conditions either from habitat change due to the population itself or from environmental change and hence this approach is potentially useful in solving certain population problems.