Phosphorus-31 magnetic resonance spectroscopy of the human liver was undertaken in 28 healthy adult individuals and in 49 patients with liver disease of varying aetiology. Data localised to the liver were obtained using chemical shift imaging techniques. The mean (+/- 1 S.D.) of the peak area ratio phosphomonoesters (PME)/phosphodiesters (PDE) in healthy adult individuals, from spectra obtained with pulse angle 45 degrees and repetition time 1 s, was 0.24 +/- 0.07. The intra-examination variability of this ratio was 20%, the intra-subject variability 27% and the inter-subject variability 32%. An increase in the PME/PDE was observed in the 31P hepatic MR spectrum from primary or secondary tumours in all 17 patients studied, which invariably represented an increase in PME/ATP and, in some cases, a reduction in PDE/ATP. The spectra did not show aetiological characteristics. A non-specific elevation in PME/PDE was also observed in the 31P hepatic MR spectra of 10 (40%) of 25 patients studied who had diffuse liver diseases, such as cirrhosis and infiltrating malignancies. The spectral pattern did not distinguish between diseases of varying aetiologies, but there was a linear correlation between increasing PME/PDE and a reduction in plasma albumin concentrations (p = 0.03). In three patients with hepatic malignancy and abnormal hepatic 31P-MRS, marked spectral changes were observed after successful treatment to debulk the tumour. Only minor changes were observed in the abnormal spectrum of a fourth patient in whom treatment was unsuccessful. Hepatic 31P-MR spectroscopy may prove useful for monitoring disease processes and treatment effects in well characterised patient populations.