Stroke is the leading cause of disability and the third leading cause of death worldwide. Lactate administration into the ischemic brain directly after blood reperfusion was found to be neuroprotective. MR with hyperpolarized (HP) probes enables in vivo realtime measurement of biochemical transformations of HP C-labeled precursors, including lactate. The aim of this study was to demonstrate the feasibility of probing HP [1- C]L-lactate metabolism in mice brain after ischemic stroke, and to study the influence of the time window after reperfusion on its conversion in order to evaluate the potential of HP lactate as a theranostic agent for stroke.