Many of the clinical features of normal pressure hydrocephalus have been ascribed to stretching of the periventricular nerve fibres. However, many patients may be asymptomatic despite considerable ventriculomegaly. To define the periventricular changes in cerebral energy metabolism we have measured local cerebral glucose utilisation in hydrocephalic and control Sprague-Dawley rats. Experimental hydrocephalus was induced by injection of kaolin into the cisterna magna of 3-week-old rats. After 3 months, the animals fed and walked normally. LCGU was measured using the 14C-deoxyglucose method of Sokoloff. Autoradiographs were prepared and isotope concentration determined by densitometry. Glucose utilisation was measured in 39 anatomically defined areas, widely distributed throughout the brain, and comparisons between hydrocephalic animals and controls (given intracisternal saline) were made by analysis of variance. It was found that there was no significant difference in glucose utilisation between the two groups of rats in any of the areas measured. Hence ventriculomegaly in the young rat does not impair LCGU in surviving periventricular tissue.