BACKGROUND CONTEXT: There is currently no therapy to repair or restore degenerated intervertebral discs. Embryonic stem (ES) cells can potentially grow indefinitely in vitro and differentiate into a variety of cell types. (1) Therefore, ES cells provide an attractive alternative to commonly used sources for deriving cells of various lineages for therapeutic purposes including cells capable of potentially producing nucleus pulposus. (2) The notochordal cell is felt to be the origin of the intervertebral disc. As this cell is replaced by terminally differentiated chondrocytes, disc degeneration begins, most likely as a result of reduced proteoglycan production and subsequent loss of water content of the intervertebral disc.