The [14C]deoxyglucose method was used to determine the rate of local cerebral glucose utilization (LCGU) in newborn and pubescent monkeys during focal motor seizures induced by injecting penicillin into the face-hand area of the right motor cortex. Seizures were studied in 3 newborn and 6 pubescent monkeys, and 3 newborn and 4 pubescent monkeys were used as controls. In controls, the pattern of glucose utilization within structures of the sensorimotor system was quite differenet at the two age levels; newborns showed far less activity, especially in the neocortex and striatum. In the monkeys with seizures, the unilateral increase in LCGU relative to the controls was greater in newborn than in pubescent monkeys except in the cerebral and cerebellar cortices. The increased glucose utilization in cortical and subcortical structures of the newborns was ipsilateral to the discharging lesin and lacked the well-defined pattern seen in the pubescent monkeys. In general, newborn brain was capable of supporting a focal motor seizure but lacked the precise clinical and electrographic expressions or efficient energy metabolism that accompany maturation of the brain at puberty.