What are disclosed are cephem compounds of the formula in which R1 denotes hydrogen, an optionally substituted alkyl, acyl, arylsulfonyl or alkylsulfonyl group or an amino-protective group which is known from peptide chemistry, R2 denotes hydrogen or an optionally substituted alkyl, alkenyl, alkinyl, cycloalkyl, aralkyl, acyl, aryl, arylsulfonyl, alkylsulfonyl or heterocyclic group, R3 denotes hydrogen, an ester group or a cation, R4 denotes hydrogen, a lower alkoxy group or a group which can be converted to this, X denotes a SO group in the R or S configuration or a SO2 group and A denotes hydrogen, an optionally substituted alkoxy or alkenyloxy group, halogen or a group -CH2Y, in which Y represents hydrogen, halogen or the radical of a nucleophilic compound, and in which the R2O group is in the syn-position, which compounds are valuable chemotherapeutic agents having a very powerful antimicrobial action against Gram-positive and Gram-negative bacteria and an unexpectedly good action against penicillinase-forming Staphilococci.