['Leptin is a hormone present in breast milk, which regulates food intake and energy metabolism.', 'To investigate whether leptin levels are different in breast-fed (BF) or formula-fed (FF) infants in the first months of life.', 'We evaluated serum leptin by radio-immunoassay and anthropometric parameters in 51 infants at the average age of 62.8+/-30 days, 25 exclusively BF and 26 exclusively FF.', 'Leptin serum values were higher in BF (7.1+/-10.4 ng/ml) than in FF (3.7+/-3.87 ng/ml) infants (p <0.05). Leptin values were higher in females (6.9+/-9.87 ng/ml) than in males (3.5+/-3.88 ng/ml) (p <0.05). No differences were found in anthropometric measurements and body mass index.'] Do breast-fed infants have higher leptin values than formula-fed infants in the first four months of life?