A case of delayed respiratory depression following an intrathecal injection of hyperbaric morphine hydrochloride is reported. This injection was made during a lumbar myelography in a 60 year old patient suffering from metastatic epiduritis unrelieved by oral or parenteral drugs. The differences in densities between the CSF, hyperbaric opiate solution and contrast medium explain the migration of the morphine hydrochloride from the lumbar thecal space to the basal cisternae, giving a fall in the responsiveness to CO2 of the brain stem respiratory centres. Parenteral naloxone did not reverse this ventilatory depression. Only the myosis and the analgesia disappeared. After 16 h of various attempts of reversal by parenteral injections, an intrathecal injection of naloxone was tried. This small dose (0.1 mg), given intrathecally, resulted in a prompt return to normal of respiratory function.