This study investigates the tissue biodistribution and blood clearance rates of intravenously administered carbon nanotubes (CNTs) functionalized with diethylenetriaminepentaacetic acid (DTPA) and labeled with indium-111 (111In) for imaging purposes. The functionalized single-walled CNTs (f-SWNT) were found to be rapidly cleared from the systemic blood circulation through renal excretion, with a half-life of approximately 3 hours. Both f-SWNT and functionalized multiwalled CNTs (f-MWNT) were excreted intact in urine, indicating their biocompatibility and lack of organ-specific accumulation. The study also highlights the importance of surface charge density on the pharmacokinetic profile of CNTs, with cationic f-SWNT showing a shorter blood circulation half-life compared to anionic f-SWNT. These findings provide valuable insights into the potential use of CNTs in therapeutic and diagnostic applications, emphasizing the need for further pharmacological investigations to optimize their delivery systems.This study investigates the tissue biodistribution and blood clearance rates of intravenously administered carbon nanotubes (CNTs) functionalized with diethylenetriaminepentaacetic acid (DTPA) and labeled with indium-111 (111In) for imaging purposes. The functionalized single-walled CNTs (f-SWNT) were found to be rapidly cleared from the systemic blood circulation through renal excretion, with a half-life of approximately 3 hours. Both f-SWNT and functionalized multiwalled CNTs (f-MWNT) were excreted intact in urine, indicating their biocompatibility and lack of organ-specific accumulation. The study also highlights the importance of surface charge density on the pharmacokinetic profile of CNTs, with cationic f-SWNT showing a shorter blood circulation half-life compared to anionic f-SWNT. These findings provide valuable insights into the potential use of CNTs in therapeutic and diagnostic applications, emphasizing the need for further pharmacological investigations to optimize their delivery systems.