The effect of epinephrine on the venous absorption of a local anesthetic (mepivacaine) from the epidural space of the dog was investigated by comparing the concentrations of mepivacaine in the azygos vein after epidural injection of 100 mg of 2 per cent mepivacaine with and without epinephrine 1:200,000. Blood flow in the azygos vein averaged 100 ml per minute. Concentrations of mepivacaine in the azygos vein reached a maximum of 10 μg/ml. At least 9 per cent of the dose of local anesthetic was removed in 30 min via the azygos vein; this was reduced to 3 per cent when epinephrine 1:200,000 was added to the anesthetic solution. It is concluded that die addition of small amounts of epinephrine to epidural local anesthetics is valuable to reduce venous absorption and favor neural blockade