Cardiac output estimations done by the pulse pressure method were compared to those done simultaneously by the dye method in pregnancy, labor, and in the early puerperium. The subjects selected were young, healthy and without edema or clinical evidence of heart disease. A total of 30 determinations was carried out on 23 subjects. Agreement within 25 per cent of the dye method was attained in 90 per cent of the blood pressure method tests.