OBJECTIVE: Using the 2-deoxyglucose method, measurements of local cerebral glucose utilization in large fetal animals are very difficult and expensive. To circumvent these problems we recently modified the 2-deoxyglucose method for use in the fetal guinea pig in utero (Berger et al., J Neurochem 1994; 63: 271-279). The present study was designed to measure the rates of local cerebral glucose utilization in fetal guinea pigs at 0.75 of gestation. STUDY DESIGN: After intravenous injection of 14C 2-deoxyglucose into the dams, local cerebral glucose utilization of the fetuses was measured from the time integral of the tracer in the maternal plasma and the autoradiographically determined concentration of the tracer in various parts of the fetal brain. RESULTS: Fetal cerebral glucose utilization was low as compared to adult animals and varied in different brain structures from 19 +/- 4 to 29 +/- 7 mumol/100 g/min. CONCLUSION: This study demonstrates the feasibility to measure local cerebral glucose utilization in undisturbed fetal guinea pigs in utero. We conclude that the low rate of cerebral glucose utilization and its small overall variability may reflect the neurological immaturity of the fetal brain.