Metrizamide, a new water-soluble contrast medium with low toxicity, was used for cranial computed tomography (computerized cisternography) in 26 patients. When injected by lumbar puncture, the pericerebral cisterns (posterior fossa and sella turcica especially), can be visualized with much greater precision than with classical computed tomography. It also allows the normal and pathological circulation of the CSF to be studied. The authors report on 6 cases of tumours of the posterior fossa, 10 cases of pituitary tumours, 2 cases of "empty" sella, 2 cases of CSF rhinorrhoea, 2 cases of normal pressure hydrocephalus, and 2 cases of syringomyelia, studied by this method. The examination was normal in 3 cases. The authors stress the rapidity, reliability, and good tolerance of this new method.