Biochemical studies have shown that during renal ischemia, lactate is built up predominantly in the medulla and less in the cortex. The authors intend to confirm such a difference in lactate concentration between these two zones of the kidney by means 1H magnetic resonance (MR) spectroscopy. In 10 rats, the authors used four-dimensional (n = 4) and three-dimensional (n = 6) spectroscopic imaging to investigate the left kidney after occlusion of the renal artery. By this technique, a map of the intrarenal lactate distribution was obtained during ischemia. It was determined that lactate concentration is indeed higher in the medulla than in the cortex, as verified by chemical analysis (17 +/- 4 versus 9 +/- 4 mumol/g). By correlating biochemical and morphologic information, localized MR spectroscopy combined with imaging is a powerful tool for investigating pathophysiologic mechanisms.