Indium-111 is an isotope of indium with a radioactive half-life of 2.80 days, making it useful as a radioactive tracer. It is made for this use by the Nordion(Canada) Inc. unit of Nordion, Inc. as indium-111 chloride solution, and shipped to several firms which sterilize the pure solution, combine it with carrier compounds if needed, and repackage it for medical and industrial uses.
Among the medical applications of indium-111 are specialized diagnostic uses:
- indium-111 labeled antibodies;
- indium-111 oxine is also useful for isotopic labeling of blood cell components, specifically the labeling of platelets for indium-111 for thrombus detection and indium-111 labelled leukocytes for localization of inflammation and abscesses, and determination of leukocyte kinetics; 
- labeling of peptides and other proteins with indium-111 to determine their uptake by rare cancers (for example, the indium-111 octreotide scan is a highly specific and powerful tool for diagnosing carcinoid tumors, paragangliomas, some ectopic pheochromocytomas and other uncommon neuroendocrine tumors).
Indium-111 decays by electron capture to cadmium-111, emitting a 0.1713 and 0.2454 MeV  gamma rays with a 2.8047 day radioactive half-life. The parent isotope of indium-111 is tin-111, with a decay mode of electron capture. Indium-111 also undergoes isomeric transition, emitting a 0.537 MeV gamma ray with a 7.7 minute half-life.
- "IN-111 FACT SHEET" (PDF). Nordion(Canada), Inc. Retrieved 23 September 2012.
- ""Octreotide Scan," Wikipedia, the Free Encyclopedia". Wikipedia.org.
- ""ENSDF Decay Data for 111-In"". National Nuclear Data Center. Retrieved 17 October 2012.
- ""Nuclide Table, Nuclide: In-111"". Korea Atomic Energy Research Institute (KAERI). Retrieved 23 September 2012.