The invention relates to O-methyl derivatives of azithromycin A of the formula (I) ##STR1## wherein Ia R.sup.1 =R.sup.2 =CO.sub.2 CH.sub.2 C.sub.6 H.sub.5, R.sup.3 =CH.sub.3, R.sup.4 =R.sup.5 =HIb R.sup.1 =R.sup.2 =CO.sub.2 CH.sub.2 C.sub.6 H.sub.5, R.sup.3 =R.sup.4 =CH.sub.3, R.sup.5 =HIc R.sup.1 =R.sup.2 =CO.sub.2 CH.sub.2 C.sub.6 H.sub.5, R.sup.3 =R.sup.5 =H, R.sup.4 =C.sub.3Id R.sup.1 =R.sup.2 =CO.sub.2 CH.sub.2 C.sub.6 H.sub.5, R.sup.3 =R.sup.4 =R.sup.5 =CH.sub.3Ie R.sup.1 =R.sup.2 =R.sup.4 =R.sup.5 =H, R.sup.3 =CH.sub.3If R.sup.1 =R.sup.2 =R.sup.5 =H, R.sup.3 =R.sup.4 =CH.sub.3Ig R.sup.1 =R.sup.2 =R.sup.3 =R.sup.5 =H, R.sup.4 =CH.sub.3Ih R.sup.1 =R.sup.2 =H, R.sup.3 =R.sup.4 =R.sup.5 =CH.sub.3Ii R.sup.1 =R.sup.4 =R.sup.5 =H, R.sup.2 =R.sup.3 =CH.sub.3Ij R.sup.1 =R.sup.5 =H, R.sup.2 =R.sup.3 =R.sup.4 =CH.sub.3Ik R.sup.1 =R.sup.3 =R.sup.5 =H, R.sup.2 =R.sup.4 =CH.sub.3Il R.sup.1 =H, R.sup.2 =R.sup.3 =R.sup.4 =R.sup.5 =CH.sub.3to their pharmaceutically acceptable addition salts with inorganic or organic acids, to a process for their preparation and to their use in the obtaining of antibacterial pharmaceutical preparations.