OBJECTIVE--To investigate the plasma vasoactive peptide (VIP) levels in pregnancies complicated by pre-eclampsia. DESIGN--A prospective clinical study. SETTING--University Department of Obstetrics, Tromsø, Norway. SUBJECTS--18 women with untreated gestational proteinuric hypertension between 32 and 40 weeks gestation (13 primigravid) and 8 women with normal pregnancies of similar gestational age. INTERVENTIONS--Fasting blood samples on two occasions, 10 min apart. MAIN OUTCOME MEASURES--Plasma VIP measured by radioimmunoassay. RESULTS--Mean maternal plasma VIP was 13.9 (SEM 1.7) pmol/l in those with pre-eclampsia and 4.4 (SEM 0.5) pmol/l in normal pregnancies (P less than 0.0001). CONCLUSION--The increased levels of VIP in pre-eclampsia may represent a powerful compensatory mechanism to restore vascular perfusion of various organs, including the uterus and placenta.