The invention comprises compounds of the formula:  <FORM:0870321/IV (b)/1> in which X is an alkylene radical having 1-7 carbon atoms, a cycloalkylene radical having 5-6 carbon atoms, or a phenylene radical, Y is an alkylene radical having 1-8 carbon atoms or a cycloalkylene radical having 5-6 carbon atoms and R is a hydrogen atom, an alkyl group having 1-3 carbon atoms, a hydroxyl group, a carboxyl group or, except when X is a phenylene group, the group of the formula:  <FORM:0870321/IV (b)/2> where Y has the meaning defined above; or an alkyl ester or salt thereof.  The compounds may be prepared by a method which includes the step of forming an alkyl ester of the general formula:  <FORM:0870321/IV (b)/3> in which X, Y and R have the meaning defined above, by reacting at a temperature of not more than 160 DEG C., 3-amino-2,4,6-tri-iodo benzoyl chloride with an amino acid alkyl ester of the formula:  <FORM:0870321/IV (b)/4> in which R11 is a hydrogen atom, an alkyl group containing 1-3 carbon atoms, a hydroxyl group, a carboxyl group or, except when X is a phenylene group, a group of the formula -NH-Y-COO alkyl where X and Y have the meaning defined above.  The reaction may be carried out in the presence of an acid acceptor and the ester groups converted to free acid or salts in the usual way. Examples describe N-(3-amino-2,4,6-tri-iodo-benzoyl)-methylamino, butylamino- and phenylamino-acetic acids, N-(3-amino-2,4,6-tri-iodobenzoyl)-b -phenylamino-, b -carboxyphenylamino-, b -hydroxy-ethylamino-, b -ethylamino-and b -butyl-aminopropionic acid and ethylenediamino- and hexamethylenediamino- N,N1-bis(3-amino-2,4, 6-tri-iodo-benzoyl)- N,N1-bis-b -propionic acid and hexamethylenediamino-N, N1-bis-(3-amino-2,4,6-tri-iodo-benzoyl)- N, N1-bis-a -butyric acid, together with their methyl or ethyl esters and sodium salts. 3-Amino-2,4,6-tri-iodo-benzoyl chloride is prepared by reacting 3-amino-2,4,6-tri-iodobenzoic acid with thionyl chloride to give 3-thionylamino-2,4,6-tri-iodo-benzoyl chloride which is converted by treatment with aqueous alkali.ALSO:An X-ray contrast composition comprises a compound of the formula <FORM:0870321/VI/1> in which X is an alkylene radical having 1-7 carbon atoms, a cycloalkylene radical having 5-6 carbon atoms or a phenylene radical, Y is an alkylene radical having 1-8 carbon atoms or a cycloalkylene radical having 5-6 carbon atoms and R is a hydrogen atom, an alkyl group containing 1-3 carbon atoms, a hydroxyl group, a carboxyl group or, except where X is a phenylene group, a group of the formula <FORM:0870321/VI/2> where X has the meaning defined above, or a non-toxic salt thereof and a non-toxic carrier therefor.  The acids or salts, e.g. sodium, lithium or diethanolamine or methylglucosamine salts may be processed with starch, talc, polyethylene glycol, starch or lactose to form tablets or the mixture may be used to make cores for dragees.  The compounds may also be used to fill gelatine capsules, possibly together with an oil which does not cause the gelatine to deteriorate.  Examples describe formulations containing as active constituent b  - N - (3 - amino - 2,4,6 - tri - iodo - benzoyl)-N-phenylamino propionic acid and its sodium salt and -N-ethylamino propionic acid, which are used to prepare tablets and dragees.