Plasma fibronectin (Fn) concentrations were measured in 472 cases of normal pregnancy and pregnancy induced hypertension (PIH), and 50 cases of normal individuals using radioimmune turbidity method. The results showed that the mean value of Fn in 390 cases of normal pregnancy with various weeks of gestation was 445 +/- 159 mg/L significantly higher than the average of 299 +/- 76 mg/L in 50 cases of normal individuals and 250 +/- 89 mg/L in 22 cases of normal women. As pregnancy progressed, the plasma Fn value increased slightly. The 82 cases of PIH had an average plasma Fn level of 783 +/- 168 mg/L, which was significantly higher than that in normal pregnancy. If plasma Fn concentrition of 600 mg/L was used as cut-off point for the diagnosis of PIH, the sensitivity reached to 83%. Plasma Fn level increased as the disease of PIH progressed. Therefore, plasma Fn concentrition could be used as a reliable indicator to the severity of PIH.