In vivo 31Phosphorus magnetic resonance spectroscopy (31P-MRS) permits evaluation of dynamic changes of individual phosphorus-containing metabolites in the liver parenchyma, such as phosphomonoester (PME), adenosine triphosphate, and inorganic phosphate (Pi). Intravenous fructose load alters phosphorus metabolites and allows assessment of liver function by 31P-MRS. 31P-MRS data obtained in alcoholic liver disease are however inconclusive. To study the hypothesis that fructose load can be used to investigate metabolic effects of ethanol ingestion, the interaction of different metabolites--i.e., fructose and ethanol--were followed in vivo. Using a 1.5 Tesla magnetic resonance system, six healthy volunteers were examined in three sessions each: a session after administration of (a) fructose only (250 mg/kg) was compared with (b) fructose load after ethanol ingestion (0.8 g/kg). A control experiment (c) was done after ethanol only. Spectra were acquired using one-dimensional chemical shift imaging with a temporal resolution of 5 min. Following a fructose load, the concomitant uptake of ethanol showed drastic changes of individual metabolic steps of the hepatic metabolism (averages +/- standard deviation). While the velocity of the net formation of PME (relative increase 0.46 +/- 0.11 without ethanol vs. 0.61 +/- 0.25 with ethanol) and the use of adenosine triphosphate (-0.13 +/- 0.03 vs. -0.16 +/- 0.03) and Pi (-0.022 +/- 0.009 vs. -0.021 +/- 0.004) were not significantly affected by ethanol uptake, a significant (p < 0.01) reduction of PME degradation (31.3 +/- 9.4 vs. 61.9 +/- 16.9 relative total area) and absence of an overshoot for Pi (10.5 +/- 4.9 vs. -7.1 +/- 5.3 relative area 13 min to 43 min) was observed after ethanol administration. Dynamic 31P-MRS allows the observation of individual steps of hepatic metabolism in situ; fructose metabolism in the human liver is slowed down by concomitant ethanol ingestion after the phosphorylation step of fructose. This could be explained by inhibition of aldolase rather than ethanol-induced changes of the hepatic redox state. Fructose load can be used to study effects of alcohol ingestion and might therefore be useful in patients with alcoholic liver disease.