Chicamycin is a new antitumor antibiotic produced by a strain of Streptomyces albus, No. J576 -99. The antibiotic is extractable into organic solvents from the fermentation broth and is obtained in two active forms, chicamycins A and B, depending upon the isolation procedure used. Chicamycin A is not a natural antibiotic but the methanol adduct of naturally produced chicamycin B. Both forms of the antibiotic have weak antibacterial activity against some Gram-positive and acid-fast bacteria. They inhibit the growth of experimental tumors such as P388 mouse leukemia.