Recent legislative changes to red fox Vulpes vulpes control practices in Britain have focussed attention on the possible impact of fox predation on economically and ecologically important species in agricultural landscapes. We compared the estimated mass of prey consumed annually against the pre-breeding biomass of prey species on a farm in southern England. Medium-sized mammals (mainly rabbits Oryctolagus cuniculus) dominated fox diet in all seasons (74% of mass ingested); birds (mainly pheasants Phasianus colchicus), small mammals (mainly field voles Microtus agrestis) and large mammals comprised 11, 7 and 6% of the diet, respectively. The mass of rabbits, wood mice Apodemus sylvaticus and bank voles Clethrionomys glareolus taken did not exceed the respective spring biomasses, indicating that fox predation was unlikely to be a significant limiting factor as all three species have a high rate of productivity. The impact on field voles was equivocal: the total mass consumed annually by foxes was equivalent to 2.7–5.7 times the estimated spring biomass, but this level of predation could be offset by recruitment. However, as field voles are a major dietary component of many predators and are likely to be confined to isolated habitat patches, the impact of predation on this species warrants further investigation. Predation on pheasants was equivalent to 34–81% of the estimated spring biomass: estimated levels of productivity derived from the literature would not have been sufficient to maintain pre-breeding population size. However, annual losses appeared to be fully compensated by immigration of reared birds from neighbouring farms. Predation on other avian taxa appeared insignificant.