Immunological adjuvants obtainable from already-known water-soluble adjuvants containing peptidoglycane fragments, which include saccharide units formed from N-acetylglucosamine and from an N-acyl-muramic acid wherein the acyl group is a glycolyl or acetyl group and to the muramyl group there are attached peptide chains, by modification of said already-known water-soluble adjuvants so that they bear acylating groups derived from physiologically-acceptable carboxylic polyacids, especially carboxylic diacids, and wherein preferably the acylating groups themselves include free carboxylic acid groups, for instance being derived from phthalic acid or succinic acid.