Regional cerebral glucose utilization (CGU), detectable by the uptake of 2-deoxy-[14C]glucose [( 14C]2DG), was examined during 3 behavioral states--slow-wave sleep (SWS), the still-alert state (SAL) and locomotion (LOC). Examination of the autoradiograms, generated by exposing the [14C]2DG incorporated brain sections to Kodak Royal X Pan film revealed a high level of uptake bilaterally and discretely in the parafascicular (PF) region during these behaviors. This pattern of [14C]2DG uptake does not correspond to any of the anatomical structures previously identified by histo- and cytochemical methods, including the [14C]2DG method. Further, optical density measurements of this region indicated that the [14C]2DG uptake was significantly lower during SWS than during SAL or LOC. The present finding is compatible with the interpretations of previous physiological and behavioral studies that there is an inhibition by cells at the PF relay to the dentate gyrus that is lowered during the SWS compared to the SAL state, thus allowing preferential brain-stem activation of the dentate gyrus.