This invention provides novel reagents for cyanating polysaccharides in aqueous or part aqueous solutions so that they may be covalently linked to proteins either directly or through a spacer. These reagents include 1-cyano-4-pyrrolidinopyridinium tetrafluoroborate (CPPT), 1-cyano-imidazole (1-CI), 1-cyanobenzotriazole (1-CBT), or 2-cyanopyridazine-3(2H)one (2-CPO), or a functional derivative or modification thereof. The examples illustrate the use of these reagents with a variety of polysaccharides and proteins showing that the methods are generally applicable.