A probe consisting of a cotton thread fitted inside a 15-cm Teflon tube with an inner diameter of 0.8 mm and connected to a transducer was used to measure the interstitial pressure in the subcutaneous tissue in six anesthetized dogs. The measurements were reproducible with a standard deviation of ±0.64 mm Hg. In six dogs the mean pressure in the subcutaneous tissue of the thorax was -2.74 mm Hg (range -3.25 to -1.99 mm Hg). After hemorrhage and dextran (10%) infusion, the mean pressure decreased by 1.70 mm Hg. After infusion of lactated Ringer's solution, the pressure increased to the control values.ADDITIONAL KEY WORDS hemorrhage dextran infusion