Addition of clindamycin to whole-cell cultures of Streptomyces coelicolor Müller resulted in the loss of in vitro activity against organisms sensitive to clindamycin. Incubation of such culture filtrates with crude alkaline phosphatase generated a biologically active material identified as clindamycin. Fermentation broths containing inactivated clindamycin yielded clindamycin 3-ribonucleotides and clindamycin 3-phosphate the structure of which was established by physicochemical and enzymatic means. Attempts to transform clindamycin to clindamycin 3-ribonucleotides by lysates or partially purified enzyme preparations from S. coelicolor have failed.