Abstract: A method of reversibly labeling a biomolecule including providing a linker molecule (11) having a first functional group (LG) with a reactive center, a second functional group (FG) with a reactive center, and a cleavable, e.g. hydrolyzable, moiety (A-B-C). The method further includes forming a covalent bond between the biomolecule (10) and the reactive center of the first functional group (LG), forming a covalent bond between a first label (L1) and the reactive center of the second functional group (FG), cleaving the cleavable moiety (A-B-C), e.g. hydrolyzing the hydrolyzable moiety, of the linker molecule (11) to remove the first label (L1) and to form a third functional group (W) with a reactive center, and forming a covalent bond between a further molecule and the reactive center of the third functional group (W) to reform the cleavable moiety, e.g. hydrolyzable moiety (A-B-C).