One hundred randomly selected nulliparous, normotensive women were subjected to the roll-over test between 28 and 32 weeks' gestation. Twenty-five women had a positive test. Thirteen of those 25 women developed pre-eclampsia requiring magnesium sulfate therapy. Eight had transient hypertension during labor requiring no therapy. Four had no evidence of hypertension during pregnancy. A false-positive rate for the 25 women with a positive roll-over test was 16 per cent. Seventy-five women had a negative roll-over test. Sixty-eight of those women had no evidence of hypertension of pregnancy. Seven had evidence of transient hypertension during labor requiring no therapy. A false-negative test was present in 10 per cent of the 75 patients with a negative roll-over test. In no case did a patient with a negative test develop pre-eclampsia. The roll-over test is recommended as a routine test for every pregnant patient between 28 and 32 weeks' gestation for the early diagnosis of hypertension of pregnancy.