A method for conjugating a saccharide to a carrier protein by condensation chemistry of carbodiimide, in which the saccharide comprises (for example, as part of its repeating unit), or has been derivatized to comprise amino and / or carboxyl groups , and wherein the carrier protein comprises, or has been derivatized to comprise, amino and / or carboxyl groups, which comprises the steps of: I) - if the carrier protein comprises both amino and carboxyl groups and the saccharide comprises amino groups well or carboxyl: a) mix the saccharide and aliquot of carbodiimide necessary to carry out the conjugation, and b) add the necessary vehicle protein aliquot for a period of 5 minutes to 6 hours, in which at least a quarter of the aliquot is added during the first half of the period and at least a quarter of the aliquot in the second half of the period； II) - if the saccharide comprises both amino and carboxyl groups and the carrier protein comprises either amino or carboxyl groups: a) mixing the vehicle protein and the carbodiimide aliquot required to carry out the conjugation, and b) adding the saccharide aliquot necessary for a period of 1 minute to 6 hours, in which at least a quarter of the aliquot is added during the first half of the period and at least a quarter of the aliquot in the second half of the period； III) - if the saccharide comprises both amino and carboxyl groups and the carrier protein comprises both amino and carboxyl groups: a) mix the carrier protein and the saccharide, and b) add the aliquot of carbodiimide necessary to carry out the conjugation over a period from 1 minute to 6 hours, in which at least one quarter of the aliquot is added during the first half of the period and at least one quarter of the aliquot in the second half of the period； and wherein: the aliquot of carbodiimide is 0.01 to 3 mg of carbodiimide / mg of saccharide； the saccharide is present in a final concentration of 0.5-50 mg / ml in step b)； the carrier protein is present i
