A new antibiotic complex has been obtained from the cultures of Streptomyces strain No. IMET 20978 isolated from the shrimp Crangon crangott L. On the basis of taxonomic studies the producing microorganism is described as Streptomyces fimicarius (DUCHÉ) WAKSMAN et HENRICI, 1948, type strain IMET 20978. The antibiotic complex, designated as griseorubin, belongs to the polycyclic C-glycosyl antibiotics. It is a red-coloured amorphous material which consists of eight closely related fractions including griseorubins A, B, C, D, E, F, G, and H. The griseorubin complex exhibits antibiotic activity against Gram-positive and -negative bacteria as well as against mycoplasma and protozoa. The griseorubin complex is also effective on leukemia L1210 and ZAJDELA ascites hepatoma.