In the course of the study on antitumor anthracyclic antibiotics, roseorubicins A and B, new members of the rhodomycin group, were isolated from the cultured broth of Actinomrccs rose oriolac:'us A 529 (IFO 13081), Actinomvices violascens A517 (IFO 12920), Act. violarus A530 (IFO 13104), Act. riolaceochrotnogenes A549 (IFO 13100) and Streptomyces purpurasccus A519 (IFG 13077). They were produced as orange-red pigments by shaking culture of the strains at 28°C for 5 days in a medium containing 4% sucrose, 2.5% soybean meal, 0.1% yeast extract, 0.25% NaCl, 0.32% CaCO3, 0.0005% CuSO4·5H2O, 0.0005% MnCl2·4H2O and 0.0005% ZnSO4·7H2O (pH 7.4), and extracted from the mycelium with acetone and from the culture filtrate with chloroform, then separated and purified via Sephadex LH-20 gel filtration. Roseorubicin A (C51H58N2O18, mp 143-147°C) and B (C36H48N2O11, mp 122-124°C) gave γ-rhodomycinone (9R, 10R) on acid hydrolysis. Thin-layer chromatography of acid hydrolysates showed roseorubicin A had rhodosamine, 2-deoxyfucose and rhodinose, while B had only rhodosamine. 13C-NMR spectra (A with 54 carbons, B with 36 carbons) and partial hydrolysis indicated roseorubicin A had a sugar chain of rhodinosyl-rhodinosyl-2-deoxyfucosyl-rhodosaminyl-rhodosaminyl, and B had rhodosaminyl-rhodosaminyl. They exhibited antimicrobial activity against Gram-positive bacteria (e.g., MIC for Staphylococcus aureus FDA209P: A 0.4 mcg/ml, B 3.1 mcg/ml; for Bacillus megaterium NRRLB-938: A <0.1 mcg/ml, B 6.2 mcg/ml), inhibited the growth of cultured L1210 cells (IC50: A 0.04 mcg/ml, B 0.06 mcg/ml), and suppressed RNA (A 0.33 mcg/ml, B 0.4 mcg/ml) and DNA (A 2.8 mcg/ml, B 2.15 mcg/ml) synthesis in L1210 cells.