Manganese-enhanced magnetic resonance imaging (MRI) is an established neuroimaging method for signal enhancement, tract tracing, and functional studies in rodents. Along with the increasing availability of combined positron emission tomography (PET) and MRI scanners, the recent development of the positron-emitting isotope Mn has prompted interest in the use of Mn as a dual-modality contrast agent. In this work, we characterized and compared the uptake of systemically delivered Mn and radioactive Mn in the rat brain for MRI and PET, respectively. Additionally, we examined the biodistribution of two formulations of Mn in the rat. In MRI, maximum uptake was observed one day following delivery of the highest MnCl dose tested (60 mg/kg), with some brain regions showing delayed maximum enhancement 2-4 days following delivery. In PET, we observed low brain uptake after systemic delivery, with a maximum of approximately 0.2% ID/g. We also studied the effect of final formulation vehicle (saline compared with MnCl ) on Mn organ biodistribution and brain uptake. We observed that the addition of bulk Mn carrier to Mn in solution resulted in significantly reduced Mn uptake in the majority of organs, including the brain. These results lay the groundwork for further development of Mn PET or dual Mn-enhanced PET-MR neuroimaging in rodents, and indicate several interesting potential applications of Mn PET in other organs and systems. Copyright © 2016 John Wiley & Sons, Ltd.