Transcutaneous oxygen tension (TcPO2), arterial oxygen tension, pulse, blood pressure, cardiac output and base excess or deficit were serially measured in 18 piglets, 7 to 14 days of age, subjected to a 35% hemorrhage and reinfusion of shed blood. Eight of 18 pigs died. There is a strong correlation between TcPO2 and PaO2 during normal flow, but a marked discrepancy develops during hemorrhage. Cardiac output, base deficit, and TcPO2 all follow a similar pattern during hemorrhage, but TcPO2 decreases more rapidly and remains at a low level in the nonsurviving animals. TcPO2, therefore, appears to be a sensitive, noninvasive indicator of low flow and the adequacy of resuscitation.