In order to evaluate the role of leptin in neonatal hematological parameters, we studied the serum concentrations of leptin in relation to blood hemoglobin, leukocyte and platelet values in 30 healthy term infants. We also studied the serum concentrations of IGF-I and IGFBP-3 in relation to leptin concentrations. The mean concentrations of leptin, IGF-I and IGFBP-3 were 1.63 +/-1.09, 24.65 +/- 10.04 and 976.05 +/- 214.50, respectively, at birth. A positive correlation was observed between leptin concentrations and birth weights of the infants. As no relationship could be found between concentrations of leptin and blood hemoglobin, leukocyte and platelet values, we could not determine any involvement of leptin in the regulation of physiologial hemoglobin, leukocyte and platelet concentrations at birth.