A 77-year-old woman with no history of epilepsy presented a probable nonconvulsive status epilepticus while receiving continuous intravenous morphine for back pain relating to vertebral metastasis of a malignant lymphoma. A generalized tonic-clonic seizure occurred a few minutes after injection of the morphine antagonist naloxone. No cerebral lesion was detected. This observation supports the notion of a possible pro-epileptogenic effect of opioid substances in association with metabolic and other toxic factors. Various hypotheses as to the complex actions of morphine and its antagonist in epileptogenesis are discussed.