Abstract: Macromolecular complexes which comprise a first and a second macromolecular moiety joined by a link derived from a linking agent having two or more reactive groups, one of these reactive groups being an activated acyl group, an isocyanate, an isothiocyanate, an iminoether, an iminothioether or an activated halogen atom attached to an aromatic ring and being capable of reacting with one of the macromolecules from which the macromolecular moieties are derived, under conditions where the remaining reactive group, or groups which is or are each an aziridine ring, an aryl azido group or a halogen atom in an .alpha.-position relative to a carbonyl group or two carbon atoms removed from a heteroatom carrying a lone pair of electrons, is or are substantially unreactive.Methods are provided for making the complexes and so are uses for the complexes. Pharmaceutical formulations containing the complex as are provided.