Soluble leptin receptor (sOB-R) modulates steady state leptin levels by preventing the hormone from degradation and clearance, and sOB-R:leptin ratio may be considered a marker of bioavailable leptin.In the neonate, dramatic changes in circulating leptin and sOB-R with a decrease in leptin by as much as 80% and increase in sOB-R by >5 folds are reported. At birth, weight and body mass index are positively correlated with plasma leptin concentrations, and one report indicated that sOB-R is inversely related to birth weight. This pattern of changes in leptin and its sOB-R and their relationship with body weight and body mass index presumably reflect the loss of placental contribution for leptin and the physiologic adaptation to lower availability of free leptin, thereby allowing an increase in energy intake to initiate the phase of rapid postnatal growth.