Fromthe culture broth of Streptomyces griseoflavus a new orange red basic antibiotic named cytotetrin complex was isolated by solvent extraction. The complex was fractionated into five active components, cytotetrins A, B, C, D and E, respectively. The physical, chemical and biological properties of each cytotetrin are discussed. They are active against Gram-positive microorganisms and some tumors. Cytotetrin is related to nogalamycin. In the course of screening for new antitumor antibiotics, it has been found that a neworange red basic antibiotic complexis produced by a streptomycete isolated from a soil sample. The organism designated as S-191 proved to be identical with Streptomyces griseoflavus "CBS-Cifferi" (Bucsav 7, 13). The antibiotic complex produced by S. griseoflavus No. S-191 is especially active against Gram-positive bacteria and moreover exhibits some antitumor activity. The components of the antibiotic complex were separated, obtained in crystalline state and identified as new antibiotics of the anthracycline family. These antibiotics were named cytotetrin complex and its single components designated as cytotetrins A, B,,