The radioactive-microsphere technique was used to determine distribution of cardiac output and regional blood flow in rhesus monkeys before and 10, 20, 40, and 80 minutes after induction of epidural anesthesia with lidocaine (1 per cent) without epinephrine. Four monkeys were studied during low epidural anesthesia (sensory level T10) and five other monkeys were studied during high epidural anesthesia (sensory level T1). During T10 epidural anesthesia. During T1 epidural anesthesia, blood flow (per 100 g tissue) to the lower extremity was significantly increased 10 minutes after induction of anesthesia. There was no other significant change in regional blood flow during T10 epidural anesthesia. During T1 epidural anesthesia, blood flow to the heart was significantly reduced at 10 minutes, blood flow to the liver was significantly reduced at 10 and 40 minutes, blood flows to kidneys and miscellaneous organs (lymph nodes, salivary glands, etc.) were significantly reduced at 10, 20, and 40 minutes, and blood flow to the brain was significantly reduced throughout anesthesia. Vascular resistance in the lower extremity was reduced in each monkey following epidural anesthesia, indicating arteriolar dilatation. Also, during both levels of anesthesia, the lungs received an increased proportion of the microspheres, suggesting an increased periopheral arteriovenous shunting of microspheres due to the arteriolar dilatation.