Using a micro-positron emission tomography (PET)/computerized tomography scanner, we have measured (18)F-fluorodeoxyglucose (FDG) uptake in interscapular brown adipose tissue (iBAT) in C57Bl/6 mice at intervals across a 24-h light-dark cycle. Our data reveal a strong 24-h profile of glucose uptake of iBAT, peaking at ~9 h into the light phase of the 12-h light, 12-h dark day. BAT is increasingly gaining attention as being involved in metabolic phenotypes and obesity, where BAT, as observed by PET analysis, negatively correlates with obesity and age. Conversely, animals that show perturbations in circadian clocks, behavior, and physiology show metabolic phenotypes. The observation of a 24-h rhythm in glucose uptake in iBAT makes this tissue a candidate site of interaction between metabolic and circadian systems.