1. The diets of sledge dogs at a British Antarctic sledging base were studied both at base and during sledge journeys, and samples of the diets and the relevant faeces were analysed. Changes in weight were related to calorie intakes. 2. The calorific requirements of sledge dogs were found to vary considerably from dog to dog and depended on the activity in which the dogs were involved. Whereas 2500 kcal/dog daily were just sufficient to maintain the body-weight of a completely idle dog, 5000 kcal/dog were insufficient to maintain the body-weight of a dog pulling a heavy sledge over long distances. 3. Seal meat was found to be the most beneficial and most satisfactorily absorbed diet. The artificial diets, pemmican and Nutrican, were adequate to maintain body-weight if sufficient supplies were available to give dogs as much as twice the routine ration, but were uneconomical in that large quantities of nutrients were passed in the faeces.