Ionic compounds of the formula ##STR1## wherein X is --CONR.sub.1 R.sub.2, --CH.sub.2 NH.multidot.Acyl or --CH.sub.2 OH; Y is --NR.sub.3 R.sub.4, --NH.multidot.Acyl or OR.sub.5 ; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 can be identical or different, and each is hydrogen, C.sub.1-6 - alkyl or C.sub.2-8 -alkyl substituted by 1-5 OH groups and/or by one C.sub.1-3 -alkoxy group, R.sub.5 is C.sub.1-6 alkyl or C.sub.2-8 -alkyl substituted by 1-5 OH groups and/or by one C.sub.1-3 -alkoxy group, and Acyl, which can be the same or different in X and Y, is C.sub.2-6 -alkanoyl or C.sub.2-6 -alkanoyl substituted by 1-4 OH groups and/or by one C.sub.1-3 -alkoxy group, or a physiologically compatible salt thereof with an inorganic or organic base, have valuable properties as X-ray contrast agents.