Metabonomics is the latest "omics" science and provides metabolic endpoints of drug toxicity, drug efficacy, and pathophysiology. With high-resolution 'H-NMR (nuclear magnetic resonance)spectroscopy on body fluids (eg, urine, blood samples) used in combination with statistical tools, metabolic biomarkers of drug toxicity can be distinguished and validated. For 2 decades, immuno-suppressant cyclosporine (CsA) has been used in transplantation medicine as a potent calcineurin inhibitor with well-known nephrotoxic side effects. The combination of CsA with novel macrolide immunosuppressants-sirolimus (SRL) or everolimus (RAD)-has proved to have a beneficial synergistic immunosuppressive effect but may also possess an increased nephrotoxic potential. 1H-NMR spectroscopy was performed on the blood from CsA-, SRL-, and RAD (alone and in combination)-treated rats to predict metabolic toxicity and to identify and quantify specific metabolic biomarkers. After 6 days of treatment with 10 mg/kg CsA, a significant increase in blood glucose, hydroxybutyrate, creatine+creatinine, trimethylamine-N-oxide (TMAO), and cholesterol as well as a decrease in total glutathione concentrations were observed. SRL (3 mg/kg) enhanced the magnitude of CsA metabolic changes (enhanced toxicity),whereas combination with RAD (3 mg/kg) partly curtailed them. Together with pharmacokinetic studies, quantitative NMR-based metabonomics represents a powerful tool for pharmacokinetic-pharmacodynamic-toxicodynamic evaluation in drug research.