Acute renal failure (ARF) induced by sepsis has a high mortality but lacks effective treatments. To develop novel therapies we must diagnose renal injury early and accurately in septic patients and identify any additional insults such as nephrotoxic drugs and ischemia. In this short review we describe our experience using MRI with dendrimer-based contrast agents in mouse models of ARF. This technique can diagnose early renal injury before serum creatinine is elevated, distinguish different ARF etiologies, track drug therapy and predict outcome. As an ARF biomarker, MRI with dendrimer-based contrast is a promising technique deserving further development.