Measurements of oxygen tension in the canine lumbar intervertebral disc, by the use of a polarographic oxygen electrode, were performed. The oxygen tension in the arterial blood was changed by regulating the oxygen concentration in the inspired air. The alterations in oxygen tension in the nucleus pulposus, as a function of distance to the vertebral endplate were determined. The response times registered in the disc matrix were relatively short (within five min.), which implies an efficient solute transport from the vertebral blood pool underneath the hyaline cartilage into the avascular intervertebral disc.