The plasma fibronectin concentration was abnormally elevated (greater than 400 micrograms/ml) in 16 of 17 normotensive gravid women who subsequently developed preeclampsia. Of this group, 13 had elevated levels detectable greater than or equal to 4 weeks before the onset of hypertension. Our results indicate that plasma fibronectin levels can be abnormally increased long before the onset of clinical symptoms and that abnormalities of this glycoprotein may be an early indication of this pathologic process.