Glioblastoma (GBM) is the most malignant primary brain tumor in adults. Aberrant glucose metabolism is considered a hallmark of cancer, via the so called ‘Warburg Effect’. MRS gives the access to study tumor metabolism. 1H MRS enables to quantify the steady state pool size and 13C MRS of hyperpolarized (HP) endogenous compounds provides real time metabolic information which is related to enzymatic activity. The aim of the present study was to examine whether changes in lactate production through glycolysis can be characterized using HP [2H7,13C6]D-glucose MRS, and if those correspond to changes in lactate pool size.