The conjunctival oxygen monitor reflects oxygen tension of the internal carotid artery without introducing the heating artifact characteristic of transcutaneous monitors. It is now being used in the ICU and the operating room to measure accurately and continuously Po2 and temperature of conjunctival tissue. We examined the effect of aging on these values in 101 healthy adult subjects. Mean conjunctival oxygen tension (58 +/- 14 torr) and temperature (34.9 +/- 0.6 degrees C) decreased significantly (p less than .01) with advancing age. Monitoring the conjunctival capillaries may prove to be a useful adjunct to patient care, but the effect of aging must be considered in any such measurement.