Abstract: This invention pertains to the surprising discovery of novel compositions and methods which selectively treat chronic pain while not significantly affecting basal nociceptive, acute pain, responses. The invention provides for compositions and methods of treating chronic pain by administering beta-endorphin-expressing recombinant expression systems such as adenovirus or adeno-associated virus into a subarachnoid or epidural space. The recombinant virus infects the pia mater connectve tissue cells and the infected cells express the fusion protein, wherein the fusion protein is secreted into the spinal cord parenchymal tissue in an amount effective to treat the chronic pain but not significantly affecting basal nociceptive responses.