Intravenously administered, multi-walled carbon nanotubes functionalized with diethylentriaminepentaacetic dianhydride (DTPA-MWNT) and radiolabeled with Indium-111 (111In), were dynamically tracked in vivo using a microSingle Photon Emission Tomography (microSPECT) scanner. Imaging showed that nanotubes enter the systemic blood circulation and within 5 min begin to permeate through the renal glomerular filtration system into the bladder. Urinary excretion of DTPA-MWNT was confirmed at 24 h post-administration. The renal clearance of DTPA-MWNT in rats reported here opens the door to the use of MWNT as components of multiple diagnostic and therapeutic modalities in development for systemic indications such as cardiovascular diseases and cancer. There has been an explosive increase in the number of nanomaterials designed for biomedical applications that has generated extraordinary interest and expectations for effective, disease-eradicating therapeutic modalities. At the same time, the toxicological burden and the pharmacological viability of such novel nanomaterials remain largely unknown, further complicating the discussion for the need of a new regulatory framework for nanomaterials. One such type of highly innovative nanomaterials is the CNT, first reported in the early 1990s by Iijima.