1. Carotid artery blood pressure and blood flow were measured and telemetered from wild giraffes ranging freely on the African plains.
2. The blood pressure ranged between 260/160 mm Hg when the animal was lying flat, and 120/75 mm Hg when it was standing upright; dp/dt at the onset of systole was 1500 mm/sec.
3. Peak systolic blood velocity measured at the same site was 60 cm/sec; during diastole velocity remained above 40 cm/sec. Calculated blood flow in the carotid artery ranged between 50cm³/sec in the prone animal, and 35 cm³/sec in the standing.
4. XY plots of the flow and pressure produced open clockwise loops which varied in shape with activity and posture; such phase differences probably reflect mechanical properties peculiar to the giraffe's arterial system.