Concentrating nikkomicin mixtures

A process for concentrating nikkomicins (X) and (Z) from a dilute impure aqueous solution thereof containing .gtoreq.0.5% of a mixture of Nikkomicin (X) and (Z) comprising bringing the solution to a pH between about 4 and 7, with acetic acid, contacting the solution with a weakly basic ion exchanger selected from the group consisting of basic macroporous or gel-like polystyrene resins which are cross-linked with divinylbenzene and which are partly or completely substituted by primary, secondary, tertiary and quaternary nitrogen groups, basic macroporous or gel-like cross-linked polyacrylamides, basic macroporous or gel-like acrylates or methacrylates which are transamidated, basic macroporous aminomethylated polystyrene cross-linked with about 6% of divinylbenzene and basic gel-like dextrans, and eluting the adsorbed material with a lower aliphatic carboxylic acid thereby to obtain a concentrated mixture of nikkomicin (X) and nikkomicin (Z).