We have used two different experimental models to examine the relationship between local cerebral blood flow and metabolism in hydrocephalus. In our first experiments local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were measured by quantitative autoradiographic methods in adult rats rendered hydrocephalic, though asymptomatic, by the injection of kaolin intracisternally at 3 weeks of age and in control animals. There were no significant differences in LCGU or LCBF in any of the 29 areas of grey matter examined, including layer IV of the cerebral cortex. Scanning across the cerebral cortex revealed an appreciable fall in LCGU and LCBF towards the inside and the outside of the mantle in control animals. Hydrocephalus had no significant effect on this "transmantle" pattern of reduction in cortical metabolism towards the periphery, but in contrast, significantly enhanced the reduction in cortical blood flow in 7 out of the 10 cortical regions examined. Hence, in this model of asymptomatic hydrocephalus there is relative uncoupling of LCBF and LCGU in the inner and outer layers of the cerebral mantle. In a study performed in congenitally hydrocephalic H-Tx rats at 10, 20 and 28 days we found that uptake of deoxyglucose was impaired in hydrocephalic rats compared with their non-hydrocephalic siblings. Small changes were seen at 10 and 21 days, but statistically significant changes were seen only at 28 days. A small reduction in LCBF was observed in all regions at 10 days, with statistically significant differences between control and hydrocephalic rats in auditory and parietal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)