S 9977-2 is a new trimethylxanthine derivative with promnesic properties. Its effects on cerebral glucose utilization and blood flow were studied by means of quantitative autoradiography. S 9977-2 was injected intravenously into adult rats at doses of 0.1, 1.0 and 10 mg/kg. At 0.1 mg/kg, S 9977-2 induced a significant increase in cerebral glucose utilization over control values in two white matter areas and in the vestibular nucleus. At 1.0 mg/kg, glucose utilization was affected in 14 areas out of the 63 studied, mainly limbic regions such as the hippocampus, raphe nuclei and locus coeruleus, as well as some posterior areas. Conversely, after the injection of 10 mg/kg S 9977-2, cerebral glucose utilization was similar to that of control rats. At the three doses tested, S9977-2 did not induce any significant variation in local rates of cerebral blood flow compared to those of controls. Likewise, S 9977-2 did not change the level of coupling between cerebral blood flow and metabolism, except at 10 mg/kg, where a relative hypoperfusion at a constant metabolic level was recorded. These data show that, at 1.0 mg/kg, S 9977-2 increased glucose utilization in hippocampal areas, an effect which may be related to the promnesic properties of this compound at the same dose. Moreover, at low doses, the lack of change in the level of coupling between cerebral blood flow and metabolism is indicative of the rather selective action of this compound, compared to that of caffeine. Thus S 9977-2 should have therapeutic effects, mainly via its promnesic properties, without having many side effects.