A new technique for producing continuous caudal epidural analgesia (CEA) and caudal subarachnoid analgesia (CSA) in adult horses (mares) without causing loss of pelvic limb function is described. A modified 17-gauge Huber-point directional needle was used to place a catheter with stylet into either the epidural or subarachnoid space at the lumbosacral intervertebral junction. The catheter was positioned at either the midsacral (S2-3) subarachnoid space or caudal portion of the sacral (S-3 to S-5) epidural space in 7 mares. The position of the catheter was confirmed radiographically. A 2% solution of mepivacaine HCl was used at an average dose of 0.061 +/- 0.013 mg/kg (1.3 +/- 0.3 ml) to produce CSA and 0.196 +/- 0.034 mg/kg (4.1 +/- 0.7 ml) to produce CEA. Onset of analgesia to superficial and deep muscular pinprick stimulation was faster with CSA than it was with CEA (8.2 +/- 2.4 minutes vs 21.4 +/- 3.8 minutes). Maximal caudal analgesia extended from spinal cord segments S-1 to coccyx during CSA and CEA. Periods of analgesia were shorter with CSA than with CEA (70.0 +/- 21.8 minutes vs 102.1 +/- 13.2 minutes). Perineal (S-4 to S-5) dermatome subcutaneous temperature was increased after epidural and subarachnoid injections of mepivacaine HCl solution. Heart rate, respiratory rate, systolic, diastolic, and mean arterial blood pressures, pulse pressure, rectal temperature, arterial blood gas tensions (PaCO2, PaO2), pHa, hematocrit, and total solid concentrations did not change significantly (P greater than 0.05) from base-line values after injection. The benefits and potential complications of CSA and CEA in horses are discussed.