New esters of cephalosporins of the formula ##EQU1## wherein R.sup.1 is a substituted or unsubstituted alkyl, cycloalkyl, aryl or heterocyclic group, R.sup.2 is S--R.sup.4 wherein R.sup.4 is a methyl, ethyl, benzyl or heterocyclic group, a xanthate, dithiocarbamate, thiouronium, azido, alkoxy, hydrogen, substituted or unsubstituted alkanoyloxy, carbonyloxy or 1-pyridinium group, R.sup.3 is ##EQU2## wherein R.sup.5 is hydrogen, methyl or ethyl, X.sup.2 is O or NH, R.sup.6 is a basic group, R.sup.7 is a substituted or unsubstituted alkyl, cycloalkyl, aryl, aralkyl or heterocyclic group, X.sup.1 is O or S, Y.sup.1 is hydrogen, a hydroxy, alkyloxycarbonyl, halogen, azido, a substituted or unsubstituted amino group, a carboxyl group, the group --COOR.sup.3, or a nitrite group, n is 0 or 1 and m is 0 or 1, useful as active ingredients of pharmaceutical preparations; processes for their preparation; and methods for the treatment of infectious diseases.