In the course of our screening program we have isolated from the culture of Actinomadura carminata carminomycin, a new anthracycline antibiotic which possessed strong antitumor activity in animal experiments. It is produced as a mixture of several active components: the more interesting ones are components 1, 2 and 3. Components 2 and 3 can be transformed by means of mild hydrolysis into carminomycin 1, which is obtained as a red crystalline hydrochloride C26H27O10N·HCl. The ultraviolet and visible spectra resemble that of daunomycin but are different. Carminomycin 1 on hydrolysis with 0.1 N hydrochloric acid yields daunosamine and an aglycone, carminomycinone. The structure of aglycone and carminomycin 1 was determined by physical-chemical methods. Structural analysis (including elementary analysis, IR, NMR, and mass spectrometry) revealed that carminomycinone differs from daunomycinone by substitution at the C4 position with a hydroxyl group rather than a methoxyl group. Animal experiments showed carminomycin 1 has strong antitumor activity: it suppressed 80% of OG-5 praestomach cancer and 95% of RL bronchogenous lung cancer in mice; against ascitic lymphatic leukemia 1210, it was twice as effective as methotrexate, with some mice surviving (vs all deaths with methotrexate or daunomycin). Unlike other anthracyclines, carminomycin 1 is well absorbed orally.