Addition of aromatic acids to the culture medium of Streptomyces caelestis results in the production of antibiotics different from the celestosaminides normally produced by the organism. The new antibiotic produced when 4-aminosalicylic acid was added to the culture medium was isolated and characterized as desalicetin 2'-(4 aminosalicylate). Although biological evaluation of this antibiotic is not complete, its in vitro antibacterial spectrum is identical to that of celesticetin. Radioactive salicylic acid added to the fermentation medium of Streptomyces caelestis was incorporated into the celesticetin molecule (I, Fig. 1), without randomization, to form the ester bond at the C-2' hydroxyl of desalicetin (II, Fig. 1)1). This finding, combined with the isolation 2,3,4) of several celestosaminide antibiotics from culture filtrates of S. caelestis suggested that different acids, added to the fermentation medium, might be utilized by the organism for the production of new celestosaminides. The present communication describes the development of a microbial process for the production of new celesticetin-related antibiotics and the isolation of a new celestosaminide, desalicetin 2'-(4-aminosalicylate) (III, Fig. 1).