<p>A carbodiimide derivative of the formula: W1-X-N=C=N-Y-W2-Z wherein W1 is an aliphatic hydrocarbon group, a substituted or unsubstituted aryl group, a heteroaryl group, a tertiary amino group or a tertiary or quaternary ammonium group; -W2-Z is a quaternary ammonium group; X and Y are each independently a single bond or an alkylene group; and Z is a biotin group as defined herein. The derivative is useful as a labelling reagent for introducing a biotin group into a nucleic acid or a protein.</p>
