Two new antibioics, triedimycins A and B closely related to oxazolomycin,1~3) have found in the culture of Streptomyces sp. MJ213-62F4 resembling Streptomyces melanosporofaciens. The organism was isolated from a soil sample collected at Nanao City, Ishikawa Prefecture, Japan and deposited at the Fermentation Research Institute, Agency of Industrial Science and Technology, Japan under the accession No. FERMP-11768. These antibiotics showed potent in vitro antitumor activity againstmurine leukemia cells, but weak antimicrobialactivity against limited bacteria. The strain was inoculated into a medium(1 10 ml) containing glycerol 2.0%, dextrin 2.0%, Bacto-Soytone (Difco) 1.0%, yeast extract (Dainippon Pharmaceutical) 0.3%, (NH4)2SO4 0.2% and CaCO3 0.2% (pH 7.4) in a 500-ml baffled Erlenmeyer flask and cultured for 48 hours at 28°C on a rotatory shaker (180rpm). The culture (each 2.2ml) was transferred into 17 flasks containing the same mediumand cultivation was carried out for 72 hoursunder the same condition described above. The antibiotics in the whole broth (1,700ml, pH 6.6) were extracted with EtOAc (1,700ml).