Thirteen pregnant women with pregnancy induced hypertension (PIH) in the third trimester, and eleven normotensive women in the third trimester were given 0.3 mg of the novel dihydropyridine calcium antagonist isradipine intravenously (iv). After drug administration, maternal systolic and diastolic blood pressure (SBP and DBP) decreased in both PIH patients and controls. In the hypertensive patients SBP was reduced from a mean of 150 to 124 mmHg (p<0.001), and in the controls from 124 to 119 mmHg (p>0.5). Corresponding figures for DBP were 99 to 83 mmHg (p<0.001) and 79 to 70 mmHg (p<0.001) respectively. The maximum effects were seen within 15 minutes. Maternal heart rate (MHR) increased significantly, in the PIH group from 79 to 93 beats per minute (bpm), and in the normotensive group from 84 to 98 bpm, respectively. Maximum effects were observed within 15 minutes, and within 90 minutes MHR returned to initial values. There was a non significant, transient increase in fetal heart rate in both groups after isradipine. Blood flow in the umbilical and arcuate arteries, expressed as the pulsatility index and the resistance index, was not significantly affected after 10 and 30 minutes in any of the women. Few, mild side effects (headache, palpitations) were observed. The results suggest that isradipine given iv, effectively lowers BP in normal pregnant subjects as well as in PIH patients without affecting uteroplacental blood flow.