Noninvasive determinations of systolic and diastolic blood pressure using the oscillometric method for pressure measurement were combined with externally recorded axillary pulse tracings to estimate end-systolic pressure in 32 neonates, infants and young children. Results were compared with central aortic pressure measurements made at the time of central aortic catheter placement. Studies were performed in patients aged 1 day to 48 months who weighed 0.9 to 18.1 kg. A wide range of systolic (41 to 141 mm Hg), diastolic (22 to 73 mm Hg) and end-systolic (30 to 111 mm Hg) pressure values were found. The mean absolute pressure differences and percent errors (pressure difference divided by central aortic pressure) were 1.8 mm Hg and 2.5% for systolic, 0.8 mm Hg and 0.8% for diastolic and 1.4 mm Hg and 2.1% for end-systolic pressure. No correlation was noted between percent error and age, weight, heart rate, cardiac index or systemic vascular resistance. The ability to perform reliable noninvasive pressure measurements should prove invaluable for clinical and research purposes. In addition, this method of end-systolic blood pressure determination enables sensitive indexes of left ventricular contractility to be measured noninvasively in small children.