The effect of aurothiomalate on the status of a wide range of low-molecular-mass endogenous metabolites in blood plasma obtained from animals treated with an intravenous dose of this second-line agent (150 mg/kg) has been assessed by high field proton Hahn spin-echo NMR spectroscopy. As well as modulating the effective concentrations of NMR-detectable biomolecules, aurothiomalate induces a time-dependent decrease in plasma levels of triacylglycerols with a corresponding elevation in the concentration of the ketone body 3-D-hydroxybutyrate, indicating an increased utilisation of fats for energy in rats treated with this 1:1 gold(I)-thiolate complex. These observations may reflect the toxic side-effects that are associated with aurothiomalate treatment.