Abstract: Derivative of 1-hydroxy-benzo-2,3,1-diazaborines which are substituted in the 2-position by a sulfo group linked to a defined aliphatic radical like alkyl or alkenyl and which may be substituted on the benzene ring by one or more lower alkyl radicals and/or halogen atoms and salts of such compounds. The pharmaceutical compositions containing these diazaborines are highly effective against gram-negative bacteria. The new compounds are prepared by reacting o-formyl phenyl boric acid, which may be substituted, with the respective aliphatic sulfonic acid hydrazide or by reacting the respective (substituted) benzaldehyde sulfonylhydrazone with a boron trihalogenide.