The present invention relates to a class of compounds and to diagnostic compositions containing such compounds where the compounds are iodine containing compounds. More specifically the iodine containing compounds are chemical compounds containing two linked iodinated phenyl groups of the general formula R—N(CHO)—X—N(R3)—R wherein X denoted an optionally substituted alkylene group, R3 denotes a hydrogen atom or an acyl function and each R denotes a triiodinated phenyl residue further substituted by hydrophilic moieties. The invention also relates to the use of such diagnostic compositions as contrast agents in diagnostic imaging and in particular in X-ray imaging, and to contrast media containing such compounds.