© 2015 Decker Intellectual Properties. This work describes the production of high-specific activity 55Co and the evaluation of the stability of 55Co-metal-chelate-peptide complexes in vivo. 55Co was produced via the 58Ni(p,α)55Co reaction and purified using anion exchange chromatography with an average recovery of 92% and an average specific activity of 1.96 GBq/jimol. 55Co-DO3A and 55Co-NO2A peptide complexes were radiolabeled at 3.7 MBq/μg and injected into HCT-116 tumor xenografted mice. Positron emission tomography (PET) and biodistribution studies were performed at 24 and 48 hours postinjection and compared to those of 55CoCl2. Both 55Co-metal-chelate complexes demonstrated good in vivo stability by reducing the radiotracers' uptake in the liver by sixfold at 24 hours with ∼ 1% ID/g and at 48 hours with ∼ 0.5% ID/g and reducing uptake in the heart by fourfold at 24 hours with ∼ 0.7% ID/g and sevenfold at 48 hours with ∼0.35% ID/g. These results support the use of 55Co as a promising new radiotracer for PET imaging of cancer and other diseases.