During lactation, both the nutritional and energetic requiremets of suckling change gradually. These changes normally are accompanied by modifications in chemical composition of the milk. We investigated the temporal course of milk composition during lactation in a precocial caviomorph rodent, the "degu', (Octodon degus) under laboratory condition. Female degus were kept in laboratory during gestation and lactation and fed with commercial food pellets. Milk was collected at three, stages of lactation: early (days 5-8, n = 12), middle (days 15-21, n = 7) and late (days 26-40, n = 6), and analyzed for protein, carbohydrates, lipids, ash, total solids and energy. Oil average, carbohydrates decreased from 3.1 +/- 0.3 % (early) to 1.1 +/- 0.3 % (late) during lactation: lipids, protein, ash, total solids and energy remained about the same. Lipids, the main component of the milk, were 17.3 % and protein remained near 4.4 %. Over lactation, total energy concentration of milk remained near 4.0 kJ mL(-1), The maintenance of milk composition during lactation may be related to the initially high energetic and nutritional requirements associated with a precocial reproductive mode.