The "Warburg effect," an elevation in aerobic glycolysis, may be a fundamental property of cancer cells. For cancer diagnosis and treatment, it would be valuable if elevated glycolytic metabolism could be quantified in an image in animals and humans. The pyruvate molecule is at the metabolic crossroad for energy delivery inside the cell, and with a noninvasive measurement of the relative transformation of pyruvate into lactate and alanine within a biologically relevant time frame (seconds), it may be possible to quantify the glycolytic status of the cells. We have examined the metabolism after i.v. injection of hyperpolarized 13 C-pyruvate in rats with implanted P22 tumors. The strongly enhanced nuclear magnetic resonance signal generated by the hyperpolarization techniques allows mapping of pyruvate, lactate, and alanine in a 5 x 5 x 10 mm(3) imaging voxel using a 1.5 T magnetic resonance scanner. The magnetic resonance scanning (chemical shift imaging) was initiated 24 seconds after the pyruvate injection and had a duration of 14 seconds. All implanted tumors showed significantly higher lactate content than the normal tissue. The results indicate that noninvasive quantification of localized Warburg effect may be possible.