A compound useful for in vivo imaging of organs and tumors is provided of formula: ##STR00001## wherein ##STR00002## is a cobalamin, ##STR00003## is derived from a corrin carboxylic acid group of said cobalamin, Y is a linking group and X is a chelating group, optionally comprising a detectable radionuclide or a paramagnetic metal ion, and n is 1-3.