During fetal life, placental tissue represents an additional source of leptin for the mother and conceptus. It has been suggested that feto-placental production of leptin may be involved in placental and fetal growth regulation. The aim of this study was to examine the correlation between leptin mRNA expression in the placenta and the concentrations of leptin in cord blood. A total of 30 healthy, pregnant women who gave birth to healthy neonates were included in the study. Maternal blood (obtained from the cubital vein) and umbilical cord blood were drawn immediately after birth. Serum leptin concentration was determined by enzyme-linked immunosorbent assay and serum insulin concentration was measured by radioimmunoassay. Leptin mRNA was measured in placental tissue by a reverse transcriptase-polymerase chain reaction. The estimated mean leptin mRNA expression in placenta was 4.65 +/- 1.83 pg mRNA/microg DNA. Leptin mRNA correlated with cord serum leptin concentrations (r = 0.3691, p = 0.045). Placental weight correlated with placental leptin mRNA (r = 0.3686, p = 0.045). The mean leptin concentration in cord serum at birth was slightly lower (3.1 +/- 1.9 ng/ml) than that found in maternal serum (3.9 +/- 1.2 ng/ml). A positive correlation was observed between cord and maternal serum leptin levels (r = 0.58, p = 0.001). The mean insulin concentration in maternal serum was not significantly higher than that in umbilical serum: 22.2 +/- 17.8 microIU/ml vs. 6.9 +/- 3.6 microIU/ml; r = 0.069, p = 0.71). Neither maternal nor umbilical insulin concentrations correlated with leptin concentration in cord or maternal peripheral serum.