The oxygen consumption [Formula: see text] of isolated segments of 40 human umbilical arteries was measured at different temperatures from 5 °C to 37 °C with a modified Fenn microrespirometer. The values varied from 8 μl/g per h at 8 °C to 70 μl/g per h at 37 °C. The Arrhenius plot was nonlinear, and the Q10 varied from 0.11 (30–40 °C) to 1.8 (20–30 °C) and 7.1 (10–20 °C). This suggests that the metabolic processes may be different at high and low temperatures. The results were consistent for at least 5 h post partum, and did not seem to vary from one segment of the cord to another.