The present invention refers to a process for the prepn. of 4-(desdimethylamino)tetracyclines, which compds. have a therapeutical application. The starting tetracyclines are treated with a methylating agent and the resulting trimethylammonium salts are reduced by electrolysis aq. soln. at acidic pH, the presence of adequate electrolyte. A direct elec. current with a potential of 0.5-1.5 V is applied between two convenient electrodes until the reaction is complete.