The maternal and newborn renal function in 84 normal pregnant women delivering at term was investigated. There was no difference between maternal and newborn plasma concentrations of urea (3.9 +/- 1.0 vs. 3.9 +/- 1.2 mmol/l) and creatinine (65.8 +/- 13.3 vs. 65.3 +/- 11.6 mumols/l). The plasma sodium and potassium concentrations were significantly higher in the newborn (139.6 +/- 4.1 vs. 136.8 +/- 5.1 mmol/l, p less than 0.001, and 5.1 +/- 1.3 vs. 4.2 +/- 0.9 mmol/l, p less than 0.001, respectively). Significant correlations were found between newborn sodium (p less than 0.02) and potassium (p = 0.0001) with maternal potassium concentrations, newborn urea with maternal urea concentrations (p = 0.0001), and newborn creatinine with maternal creatinine concentrations (p = 0.0001), gestation of delivery (p less than 0.05) and birth weight (p = 0.025).