Abstract: Ligands with three or more nitrogen atoms incorporated into a linear or cyclic backbone structure, with the nitrogen atoms substituted with a combination of phosphonate groups and nonphosphonate groups, of which at least two are phosphonate groups, are disclosed. These ligands are combined with paramagnetic metal cations and administered in the form of pharmacologically acceptable salts, are useful as MRI contrast enhancement agents, which tend to localize in bone tissue without being conjugated to bone-specific biomolecules. Triazacyclononanes and tetraazacyclododecanes, with dihydroxyphosphorylmethyl or dihydroxyphosphorylethyl groups linked to the backbone nitrogens are preferred.