The new, belonging to the streptothricin-group antibiotics AN-201 I, II and III were found to be produced by a soil actinomycete identified as Streptomyces nojiriensis C-13. The chemical structures and the physical and spectroscopic properties of these compounds are reported here. On the basis of NMR and fast atom bombardment mass spectrometry (FAB-MS) spectra the antibiotics were identified as N beta-acetylated derivatives of streptothricins E, D and F.