Milk consumption was measured in pouch young of the northern brown bandicoot, Isoodon macrourus, using the 22Na turnover technique. Milk consumption rates increased from about 2.3 ml young−1 d−1 at 23 days post-partum to about 17.2ml young−1 d−1 at 52 days, just prior to weaning. Young increased in mass from 8.5 g to around 112 g over the same period. Masś gained for each ml of milk consumed ranged from 0.28 to 0.65 gml−1. The efficiency with which young converted milk energy and protein into body energy and protein ranged from 16.1 to 39.6% and 38.4 to 82.3%, respectively.