The adverse effects following lumbar myelography and ventriculography with meglumine iothalamate (Conray Meglumin), meglumine iocarmate (Dimer-X, Bis-Conray) and metrizamide (Amipaque), and after thoracic and cervical myelography and cisternography with metrizamide are reviewed. In addition to the published material information given to Nyegaard & Co. from several hospitals participating in clinical trials with metrizamide is also reported. The frequency of minor adverse effects (headache, nausea, vomiting) seems to be about the same with all the three water-soluble contrast media. Convulsions, either localized to the lower part of the body or generalized, may be a problem with meglumine iothalamate and meglumine iocarmate, while the epileptogenic effect is markedly lower with metrizamide. With a technique directed towards preventing contrast medium of high concentration from passing intracranially, the frequency of serious adverse effects may be kept at a very low level. Late adverse effects (adhesive arachnoiditis) occurring after all other water-soluble contrast media are a very minor problem after metrizamide. Serious complications have not been recorded following ventriculography and cisternography with metrizamide. Metrizamide is considered to be the water-soluble contrast medium best suited for use in the subarachnoid space and cerebral ventricles.