Liver metabolism of two patients (aged 15 and 23 yr) was studied by P-31 magnetic resonance spectroscopy at 1.9 tesla. The P-31 spectra of liver showed the resonances of phosphomonoesters (including sugar phosphates), inorganic phosphate (Pi), phosphodiesters (e.g. glycerophosphorylcholine, glycerophosporylethanolamine), and ATP. These resonances were quantified by expressing their peak areas in mM (assuming that ATP concentrations in normal liver is 2.5 mM) or as a ratio relative to the area of the phosphodiester resonance. After an overnight fast liver phosphomonoesters in patients were 2.6 and 1.6 AU, respectively (controls 1.1 +/- 0.5, mean +/- 2 SD, n = 17). At the same time liver Pi was decreased in patients to 1.3 and 1.0, respectively (controls 1.8 +/- 0.8). Based on chemical shift measurements the increase in phosphomonoesters could be attributed to accumulation of sugar phosphates (mainly glycolytic intermediates). After 1 g/kg oral glucose, hepatic sugar phosphates decreased in patients by 64 and 40%, respectively, and reached normal levels (on the absolute intensity scale); whereas liver Pi increased by 130 and 40%, respectively. Liver Pi levels remained elevated in both patients 30 min after ingestion of glucose. Liver sugar phosphates and Pi did not change in control subjects (n = 4) after glucose. In contrast to some previous reports, we have found accumulation of glycolytic intermediates in the liver of glucose-6-phosphatase-deficient patients during fasting. In these patients high levels may enhance the activity of residual glucose-6-phosphatase thus increasing hepatic glucose production and reducing the degree of hypoglycemia during fasting.(ABSTRACT TRUNCATED AT 250 WORDS)