The consequences of a chronic neonatal diazepam (DZP) treatment on the postnatal evolution of various aspects of cerebral energy metabolism and on behavior were studied in suckling rats. Animals were treated from postnatal day 2 to 21 by a daily subcutaneous injection of DZP (Valium injectable, Roche) at the dose of 10 mg/kg. Control animals received the same volume of the dissolution vehicle. Measurement of the incorporation of glucose carbon into cerebral amino acids and local cerebral glucose utilization were assessed at 5, 10, 14 and 21 days while behavioral testing was performed at 4, 9, 10 and 20 days. DZP exposure induced a decrease in body weight during the whole period studied as well as a delay in hair appearance. Circulating concentrations of glucose were reduced whereas those of ketone bodies were not affected by the treatment. Incorporation of glucose into amino acids was reduced at 5 and 10 days in the three brain regions studied and local cerebral glucose utilization was decreased essentially in sensory, motor and cortical areas during the same period of development. DZP treatment did not impair rat performances for the righting reflex, swimming or climbing a vertical rod. Conversely, DZP increased the time necessary to the rats to pivot by 180° on an inclined plane and altered their balance abilities, data that are in accordance with the decreases in functional activity in structures controlling balance and visuo-motricity. Finally, DZP prolonged the suspension time at 10 days, certainly as a result of its muscular relaxation properties.