The maintenance nitrogen requirement (MNR) of the rufous rat-kangaroo (Aepyprymnus rufescens) was determined in a series of balance studies, with animals fed cereal/oat-hull diets varying in their content of nitrogen (5.8-17.0 g N per kg dry matter) and plant-cell walls (fiber). Nitrogen balance was not affected by the level of dietary fiber. Consequently, the data were pooled to give a truly digestible MNR of 199 mg per per d for animals fed grain-based diets with neutral detergent fiber levels between 100 and 300 g per kg dry matter. Nitrogen balance data from experiments with two other potoroine marsupials divided by Potorous tridactylus (long-nosed potoroo) and Bettongia penicillata (brush-tailed bettong) suggested that their MNRs are similar to those of A. rufescens. A comparison of these results with those published for other species showed that the MNRs of potoroine marsupials are markedly less than those of most eutherians. Less expected was the finding that the MNRs of potoroine marsupials are similar to those of some arid-zone marsupials. Nitrogen balance measurements made on A. rufescens with pouch young indicated that total N requirements of breeding females were about four times those for maintenance of adult male animals. A diet of relatively high N content (22 g per kg dry matter) was fed throughout lactation. Thus, the estimated N requirement is realistic for animals at peak lactation but probably overestimates the requirements of those in early lactation.