The real-time metabolic transformation of lactate in the mouse head was monitored following the injection of hyperpolarized 1-13C lactate at physiological doses. The results were compared with metabolic studies performed with hyperpolarized 1-13C pyruvate at similar blood concentration. From the observation that the lactate to alanine ratio was nearly identical following both the pyruvate and the lactate injections, we concluded that the substrate and its metabolites can be detected in real time at physiological concentrations after the injection of lactate.