OBJECTIVE Pregnancy induced hypertension has been shown to be associated with a normal or low activity of the maternal circulating renin–angiotensin system (RAS) but little is known of the local RAS in placenta and fetal membranes. The present study attempts to determine, at full term of human preeclamptic pregnancies, the activity of the chorioplacental renin–angiotensin system.PATIENTS AND MEASUREMENTS We analysed the concentrations of active renin, prorenin, angiotensin converting enzyme (ACE) and angiotensin II in homogenates of human placenta and fetal membranes from preeclamptic patients at full term pregnancy. The values of renin, ACE and angiotensin II found in the patients with moderate preeclampsia (gestosis index 0–1) (n = 10) were compared with those of normal pregnant women (n = 8).RESULTS Our experiments showed that in preeclamptic pregnancies, the chorion membrane contained the highest concentrations of active renin (2905 ± 152 pg/g, mean ± SD), prorenin (21 315 ± 2849 pg/g) and ACE (1258 ± 302 U/g) whereas the placenta had more angiotensin II than the chorion and amnion (741 ± 45vs456 ± 40 and 428 ± 64 pg/g, respectively). In the placenta, as in the fetal membranes, no significant difference was found in the levels of active renin, ACE or angiotensin II between hypertensive patients and normal subjects but a slightly lower level of chorionic prorenin (P < 0.05) was observed in pregnancy induced hypertension.CONCLUSION These findings indicate that in moderate preeclampsia (gestosis index 0–1), the activity of the renin–angiotensin sy