This study investigates the tissue biodistribution and blood clearance rates of intravenously administered carbon nanotube (CNT) radiotracers. Water-soluble, single-walled CNT (SWNT) were functionalized with the chelating molecule DTPA and labeled with indium-111 for imaging. Intravenous administration of these functionalized SWNT (f-SWNT) showed rapid clearance from systemic blood circulation through the renal excretion route, with a half-life of 3 hours. Urine excretion studies revealed that both f-SWNT and functionalized multiwalled CNT were excreted as intact nanotubes. The study highlights the pharmacokinetic parameters of i.v. administered functionalized CNT relevant for therapeutic and diagnostic applications. The study also examined the in vivo behavior of functionalized CNT, including their toxicological and pharmacological profiles. The results showed that f-SWNT and f-MWNT were not retained in the reticuloendothelial system organs (liver or spleen) and were rapidly cleared from the blood. The high levels of indium-111 found in the kidney after 30 minutes and the rapid decline in radioactivity levels indicated that most of the nanotubes were eliminated through the renal excretion route. The blood clearance half-life of f-SWNT was found to be approximately 3 hours, which is significantly shorter than that of other functionalized C60 fullerenes. The study also demonstrated that f-SWNT and f-MWNT were excreted as intact nanotubes in urine, indicating that they are cleared from systemic blood circulation through the renal excretion route. The results suggest that functionalized CNT have a significantly improved toxicity profile compared to their nonfunctionalized counterparts. The study provides previously undescribed pharmacokinetic data after i.v. administration of CNT, exhibiting a blood circulation half-life of up to 3.5 hours. The findings have important implications for the development of CNT-based delivery systems for therapeutic and diagnostic applications.This study investigates the tissue biodistribution and blood clearance rates of intravenously administered carbon nanotube (CNT) radiotracers. Water-soluble, single-walled CNT (SWNT) were functionalized with the chelating molecule DTPA and labeled with indium-111 for imaging. Intravenous administration of these functionalized SWNT (f-SWNT) showed rapid clearance from systemic blood circulation through the renal excretion route, with a half-life of 3 hours. Urine excretion studies revealed that both f-SWNT and functionalized multiwalled CNT were excreted as intact nanotubes. The study highlights the pharmacokinetic parameters of i.v. administered functionalized CNT relevant for therapeutic and diagnostic applications. The study also examined the in vivo behavior of functionalized CNT, including their toxicological and pharmacological profiles. The results showed that f-SWNT and f-MWNT were not retained in the reticuloendothelial system organs (liver or spleen) and were rapidly cleared from the blood. The high levels of indium-111 found in the kidney after 30 minutes and the rapid decline in radioactivity levels indicated that most of the nanotubes were eliminated through the renal excretion route. The blood clearance half-life of f-SWNT was found to be approximately 3 hours, which is significantly shorter than that of other functionalized C60 fullerenes. The study also demonstrated that f-SWNT and f-MWNT were excreted as intact nanotubes in urine, indicating that they are cleared from systemic blood circulation through the renal excretion route. The results suggest that functionalized CNT have a significantly improved toxicity profile compared to their nonfunctionalized counterparts. The study provides previously undescribed pharmacokinetic data after i.v. administration of CNT, exhibiting a blood circulation half-life of up to 3.5 hours. The findings have important implications for the development of CNT-based delivery systems for therapeutic and diagnostic applications.