Even though invasive intrauterine techniques for the treatment of TTTS such as punction of amniotic fluid and laser coagulation of placental vascular anastomoses are established methods in specialized centers, invasive methods are not always sufficiently successful. In conservative treatment of TTTS oral or intravenous maternal digoxin therapy in order to improve fetal cardiac insufficiency in combination with or after failure of invasive techniques is an useful method.We investigated 12 TTTS pregnancies and 4 singleton pregnancies, which had been treated by maternal digoxin treatment for TTTS or arrhythmias, respectively. At birth, which was performed by means of caesarian section, venous cord blood samples of the newborns and venous maternal blood samples were collected, centrifugated and stored at minus 20 degrees C. Digoxin determinations were performed by radioimmunoassay.Fetal digoxin levels varied between 0.38 and 1.73 ng/ml, maternal levels ranged from 0.97 to 3.23 ng/ml. The fetomaternal digoxin gradient reached a mean of 0.56 (range 0.35 to 1.09). Donator and acceptor gradients were comparable and increased with birth weight or gestational week, respectively.In cases of pregnancies with TTTS a relatively high maternal digoxin level is necessary, especially during early gestational weeks, in order to reach therapeutical levels in the fetal circulation. Too low dosages might be responsible for unfavourable results in digoxin treatment of TTTS. Whether the maturation of placental villi during gestation could be the reason for increasing digoxin gradients requires further investigations.