Voluntary intake responses of neonatal lean and obese pigs, fed high and low energy diets, were measured. Piglets were maintained in individual cages from 4 to 22 days of age. The 18-day trial was divided into six 3-day ad libitum feeding periods. All piglets received a purified high energy diet (1.12 kcal/ml) in periods 1, 3, 5, and low energy diet (0.57 kcal/ml) in periods 2, 4, and 6. Average daily volume intakes for periods 1 to 6 were 36.8, 55.2, 41.4, 56.2, 38.4, and 47.8 ml/100 g body weight (BW), respectively. Average daily energy intakes were 40.5, 28.7, 45.5, 29.2, 42.2, and 24.9 kcal/100 g BW. Even though piglets consumed greater volumes of low energy diet, energy intake was not maintained during periods 2, 4, and 6. It is possible that gastrointestinal capacity limited intake before energy demand was met. Compared to lean piglets, obese piglets were hyperphagic and consumed more volume (52.0 versus 39.8 ml/100 g BW/day) and more energy (40.0 versus 30.4 kcal/100 g BW/day). It is conclused that neonatal lean and obese piglets possess a sensitive mechanism (s) to control food intake in response to changes in energy content of the diet. The control mechanism in the obese piglets appears to function at a higher level of energy demand than in the lean piglets.