8006-I is an antibacterial antibiotic with a rather broad spectrum of activity. The minimum inhibitory concentrations for the most sensitive bacteria are in the range of one to ten μg/ml. Yeasts are not affected by concentrations up to 100 μg/ml. Some filamentous fungi like Fusarium oxysporum and Mucor miebei are inhibited at 100 μ g/ml. In Ehrlich carcinoma ascitic cells the incorporation of uridine and leucine and to a lesser extent that of thymidine is reduced. In isolated nuclei of these cells the incorporation of UTP into RNA is inhibited. At low concentrations, the incorporation of uracil into trichloroacetic acid-precipitable material is almost completely inhibited in cells of Bacillus subtilis; at higher concentrations all macromolecular syntheses are affected. No reduction of respiration of the cells is observed. The antibiotic exhibits weak hemolytic activity and lytic activity towards bacteria. In vitro an inhibition of both DNA- and RNA polymerase from Escherichia coli is observed. Poly(U)-directed poly(Phe) synthesis is not affected.