Conray ventriculography is a method for the roentgenographic visualization of the cerebral ventricular system with meglumine iothalamate 60%(Conray). Although it has been known that ventriculography using Conray 60% offers definite advantages compared to that with other contrast media and untoward reactions have been reported as mild and transitory ones, a significant disadvantage is the possible development of seizures. Recently we had performed Conray ventriculogrqaphy and analized their untoward reactions in 25 cases which were previously proved hydrocephalic by cerebral angiographies, from march, 1973 to August, 1974. They included twenty cases of brain tumor and five cases of hydrocephalus. Untoward reactions were analized with respect to the different concentration of the contrast media used, communicating or noncommunicating pathway of the cerebrospinal fluid and the different sites of obstruction in the cerebrospinal fluid pathway. The results were as follows: 1. Headache and convulsion were more frequently observed in cases of ventriculography using undiluted Conray. 2. High frequency of vomiting was observed in cases with communicating pathway of the cerebrospinal fluid. 3. There seemed to be no difference in untoward reactions between the levels of obstruction in the cerebrospinal fluid pathway.