WHILE studying the antibacterial products of a species of Streptomyces (N.C.I.B. 8697) sent by Dr. R. Green from Malaya, we have isolated an orange-red coloured basic substance which is very active against a variety of bacteria and is highly toxic to mice. The antibiotic was extracted from the culture fluid into chloroform, at pH 6, and re-extracted into water at pH 2, or extracted into trichloroethylene, at pH 8.5, and re-extracted into water at pH 3.5. It was purified by counter-current distribution in a solvent system consisting of trichloroethylene and 0.1 M sodium citrate buffer, pH. 5.95. In this system its partition coefficient, K (Combining double low line concentration in trichloroethylene/concentration in water), was 0.98. The purified product yielded a crystalline hydrochloride, reineckate and picrate. The behaviour of this antibiotic suggests that it is identical with, or very closely related to, xanthomycin A - a substance which has been isolated from species of Streptomyces1, and stated to have quinonoid properties2. We wish to record, however, that it is a stronger base than xanthomycin A has been reported to be and that it yields two simple bases on hydrolysis which have not been described as degradation products of xanthomycin A. © 1955 Nature Publishing Group.