Creatinine concentration in the amniotic fluid (A.F.) of pre-eclamptic patients without treatment with furosemide was compared to the values obtained in normal pregnant women at the same stage of gestation. These values increased significantly when a diuretic treatment was started; no correlation was found with either maternal serum level or the A.F. volume. Furosemide treatment had no significant effect on A.F. volume in the pre-eclamptic group.