We determined the regional relationships of the lumped constants for deoxyglucose (DG) and fluorodeoxyglucose (FDG). Awake male rats were given simultaneous intravenous injections of [14C]DG and [18F]FDG, and sacrificed after 45 min. The brains were removed and small pieces of cortical tissue were sampled by dissection. The remainder of the brains were frozen and sliced into 20-microns-thick sections that were placed on coverslips and dried on a hot plate. Two sets of brain autoradiograms were prepared from the brain sections, one representing predominantly [14C] and the other [18F]. The autoradiograms were digitized, and after correcting for cross-contamination, tracer-concentration images of the DG and FDG were generated. Based on relative tracer concentrations in the tissue samples, the lumped constant of FDG was found to be 1.25 times that of DG, or 0.6. Using this value, images of glucose metabolism for the DG and FDG were generated from the tracer concentration images and compared. No significant regional differences were found, indicating that the relationship between the lumped constant of DG and that of FDG was stable throughout the normal brain.