In this study, acute effects of cadmium ions (Cd2+) on energy metabolism in rat livers were analyzed in vivo after intravenous administration using 31P NMR. Both inorganic phosphate (Pi) and nucleotide triphosphate (NTP) peaks of in vivo Cd-treated livers gradually decreased over a 6-h period. In the extract, NTP peaks in Cd-treated livers were lower, as in the in vivo experiments, but the Pi peak was significantly higher than the control. The apparent decrease in Pi in in vivo liver treated with Cd could be caused by the reduced visibility of Pi because of its uptake into mitochondria from cytoplasm, accompanied by the uncoupling of oxidative phosphorylation by Cd2+. These results indicated that total Pi in the hepatocytes increases after Cd administration. However, only 10% of Pi was visible in Cd-treated livers in vivo, whereas 34% of Pi was visible in controls. Significant increases in phosphocholine and glycerophosphocholine were also observed in extracts of Cd-treated livers.