Abstract: A process for the preparation of cefodizime of the formula ##STR1## wherein (a) a compound of the formula II (ATS) ##STR2## wherein R.sub.1 represents hydrogen or an aminoprotective group and A represents a hydrogen atom or one equivalent of an alkali metal or alkaline earth metal, of ammonium or of an organic nitrogen base, is first reacted with a compound of the formula IIIR--SO.sub.2 Halwherein R represents an optionally substituted alkyl, aryl or aralkyl radical and Hal represents a halogen atom, in an organic solvent and, if appropriate, in the presence of a base,(b) a compound of the formula I (TACS) ##STR3## in which A has the above meaning, is reacted with a silylating agent in an organic solvent and, if appropriate, in the presence of a base, and(c) the two products formed in (a) and (b) are reacted in their reaction solutions, and any protective group R.sub.1 present in the end product of the formula I is eliminated.