Hydrolysis of teicoplanin (a complex of five closely related factors plus one, more polar component) under selected conditions (acids in a biphasic hydroalcoholic medium) gives the single aglycone with good yields. When the reaction is carried out in homogeneous hydroalcoholic phase the removal of the sugars yields two new compounds. On the basis of fast atom bombardment mass spectra (FAB-MS), acid-base titration, IR, UV and 1H NMR analyses it has been demonstrated that these compounds are two diastereoisomers; they differ from the teicoplanin aglycone in having additional carboxyl and amino groups derived from the hydrolysis of an amide bond. Although the molecular shape of the new aglycones is greatly modified, they still maintain some antibacterial activity which might be correlated with residual binding ability towards the terminal D-alanyl-D-alanine residue of the cell-wall mucopeptides.