Maternal plasma levels of cortiocotrophin-releasing factor (CRF) have been measured in abnormal pregnancy states to assess their potential as biochemical markers for at-risk pregnancies. CRF levels were not significantly altered in patients with hydatidiform mole, polyhydramnios or diabetes. CRF levels were elevated in pregnancies complicated by accidental antepartum haemorrhage at 28 weeks (P less than 0.03) but not for the rest of the third trimester. In twin pregnancies CRF levels were significantly raised throughout the third trimester (28-32 weeks, P less than 0.01; 34-36 weeks, P less than 0.001). In patients with pregnancy-induced hypertension (28 weeks, P less than 0.001; 32-36 weeks, P less than 0.001; and 38-40 weeks, P less than 0.01), preterm labour and premature rupture of the membranes (28 weeks, P less than 0.004; 30-32 weeks, P less than 0.002; and 34-36 weeks, P less than 0.001), CRF levels were significantly raised and in some patients levels were elevated 11 weeks before the onset of signs or symptoms. These observations raise the possibility that maternal CRF measurement may be of use as a predictive indicator of certain at-risk pregnancies.