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(CO—CH3)XN(CO—CH3)—R and salts or optical active isomers thereof, wherein X denotes a divalent linking moiety with 5 to 10 bridge elements of carbon, oxygen, sulphur and nitrogen separating the acetylated nitrogen atoms, and which may be further substituted by hydroxyl groups, by C1 to C4 alkyl moieties optionally substituted by hydroxyl groups, by C1 to C4 alkoxy groups, by amino groups and by C1 to C4 alkylamino groups, and wherein 2 or 3 carbon bridge elements together with alkyl or alkoxy groups form a cyclopentane, cyclohexane, pentahydropyran or tetrahydrofuran entity which may be alkyl- or hydroxyalkyl-substituted 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.