Four novel cyclic homodecapetide antibiotics, streptocidins A-D were detected in the mycelium extract of Streptomyces sp. Tü 6071 by HPLC-diode-array and HPLC-electrospray-mass-spectrometry screening. The peptides which were closely related in structure to the tyrocidines and gramicidins of Bacillus brevis show antibiotic activities against Gram-positive bacteria.