The invention relates to a conjugate which comprises an MRI contrast agent component comprising a nanoparticle, which nanoparticle comprises a metal or a metal compound, and a hypoxia targeting moiety which is conjugated to the MRI contrast agent component, especially wherein said nanoparticle comprises iron oxide and a biocompatible coating and wherein said hypoxia targeting moiety is a nitroimidazole. Also provided is the use of a said conjugate in a method of imaging a subject, a method of de-testing hypoxia, and a method of evaluating the activity of a pharmaceutical. Said conjugate is also of use in diagnosis.
