Selection for high or low daily food intake (DFI) in Large White pigs resulted in higher serum leptin concentration, fat deposition and food intake in the high DFI line. The response in serum leptin concentration indicated that the higher fat deposition of the high DFI line was not due to insufficient leptin production, as in the Lepob/Lepob mouse. Serum leptin was more highly correlated with fat deposition than with food intake indicating that the response in serum leptin was primarily due to increased fat deposition rather than to higher energy intake per se. The low correlations between serum leptin measured at 30 kg and performance test traits indicate that serum leptin would not be efficient for selection of animals prior to performance test. However, the consistent positive correlations between serum leptin and a measure of fat deposition suggest that serum leptin could usefully be incorporated in selection criteria for genetic improvement of carcass lean content in pigs.