31P NMR spectroscopy was used in conjunction with conventional biochemical techniques to study metabolic abnormalities in normal rats, in rats with CCl4-induced acute liver failure and in rats with paracetamol-induced acute liver failure. Studies were carried out before and after a metabolic challenge in the form of a fructose infusion. Prior to fructose infusion the ATP levels in the groups with acute liver failure were significantly lower than in control rats, despite their having a similar ATP/Pi ratio. Following a fructose infusion in control animals, the changes in phosphomonoesters, ATP and inorganic phosphate were consistent with previously reported findings. However, in both test groups the percentage changes in phosphomonoesters and ATP were significantly smaller. Intracellular pH declined in control animals, but did not change significantly in the animals with acute liver failure. Fructose clearance from the blood in control animals was not significantly different from that in animals with CCl4-induced acute liver failure. Metabolic changes measured using a horizontal magnet were very similar to those obtained with a vertical magnet.