Dihydroxy benzene sulphonic acid-formaldehyde polycondensation products useful as antiulcer agents comprise more than one unit of formula <FORM:0839391/IV (b)/1> in which X represents a hydrogen atom or a hydroxyl group, Y represents a hydrogen atom, a hydroxyl group, a halogen atom or an alkyl group having 1 to 8 carbon atoms, and R represents a hydrogen atom or an alkaline earth metal or alkali metal cation, with the proviso that when Y is a substituent other than a hydrogen atom or a hydroxyl group, the sulphonic acid group and the substituent Y are in para-position relatively to each other, and that, when X is a hydrogen atom and Y is a hydroxyl group, the hydroxyl groups are in ortho-position relatively to each other and the sulphonic acid group is in ortho-position thereto, and that one of the residues X or Y is an hydroxyl group.  The polycondensation product may be prepared by treating the monomer starting material, e.g. 2 : 5 - dihydroxy-4-chlorobenzene sulphonic acid, with formaldehyde, preferably in an alkaline medium of pH9 or above, refluxing the mixture for 1 to 8 hours, and precipitating the polymer in the form of its salt by addition of an organic solvent.  The free acid of the polymer is obtained by acidification of the salt form with any suitable inorganic or organic acid.  Examples of polycondensation products are given.ALSO:Dihydroxy benzene sulphonic acid-formaldehyde polycondensation products, comprise more than one unit of formula <FORM:0839391/IV (a)/1> in which X represents a hydrogen atom or a hydroxyl group, Y represents a hydrogen atom, a hydroxyl group, a halogen atom or an alkyl group having 1 to 8 carbon atoms, and R represents a hydrogen atom or an alkaline earth metal or alkali metal cation, with the proviso that when Y is a substituent other than a hydrogen atom or a hydroxyl group, the sulphonic acid group and the substituent Y are in para position relatively to each other, and that, when X is a hydrogen atom and Y is a hydroxyl group, the hydroxyl groups are in ortho position relatively to each other and the sulphonic acid group is in ortho position thereto, and that one of the residues X or Y is a hydroxyl group.  The polycondensation product may be prepared by treating the monomer starting material, e.g. 2,5-dihydroxy-4-chloro-sulphonic acid, with formaldehyde, preferably in an alkaline medium of pH 9 or above, refluxing the mixture for 1 to 8 hours, and precipitating the polymer in the form of its salt by addition of an organic solvent.  The free acid of the polymer is obtained by acidification of the salt form with any suitable inorganic or organic acid.  Examples of polycondensation products are given.ALSO:A therapeutic preparation for the treatment of gastro-intestinal ulcers, comprises a dihydroxy-benzene sulphonic acid-formaldehyde polycondensation product having more than one unit of formula <FORM:0839391/VI/1> in which X represents a hydrogen atom or a hydroxyl group, Y represents a hydrogen atom, a hydroxyl group, a halogen atom or an alkyl group having 1 to 8 carbon atoms, and R represents a hydrogen atom or an alkaline earth metal or alkali metal cation, with the proviso that, when Y is a substituent other than a hydrogen atom or a hydroxyl group, the sulphonic acid group and the substituent Y are in para position relatively to each other, and that, when X is a hydrogen atom and Y is a hydroxyl group, the hydroxyl groups are in ortho-position relatively to each other and the sulphonic acid group is in ortho-position thereto, and that one of the residues X or Y is a hydroxyl group, and a pharmaceutical carrier.  The preparation may take the form of tablet, capsule, pill, solution, powder or other dosage unit and may contain from 0.1 gram to 3.0 gram of the polycondensation product.  Examples of the polycondensation products are given. Examples of pharmaceutical carriers, which may be solid or liquid, are tragacanth, corn starch, lactose, magnesium stearate, talcum, sodium benzoate, sugar, and glycerine.