A computerized system has been developed to continuously monitor, collect and display pO2 in real time from the maternal and fetal arteries and veins in the dually perfused term placenta. Oxygen electrodes were installed in flow-through chambers in the tubing of the perfusion system. The signal from the O2 electrodes was digitized, acquired, analyzed and displayed in real time during the perfusions using a personal computer. Output from the O2 electrodes was linearly proportional to pO2 (33-502 mm Hg; r2 = 0.99). Running average pO2 values (mean +/- SD) were also calculated for every minute and stored. The captured data files can be recalled and analyzed after completion of the perfusion experiment and compared with other data collected during perfusion. One of the unique capabilities of the pO2 electrodes is their ability to respond rapidly to changing perfusion conditions. For example, as the fetal circulation begins to break down the change is noted before volume loss in the fetal circuit by decreasing fetal vein pO2.