Gentamicin, an aminoglycoside antibiotic, occurs both free in the fermentation filtrate and bound to the mycelium of the producing organism, Micromonospora purpurea. The bound gentamicin, which represents the major portion of the total quantity present in the fermentation broth, was released after exposure to acid, alkali, or sonic disruption. Washing the mycelium with distilled water, heat treatment, and the addition of sodium chloride to the fermentation medium were not effective methods for releasing bound gentamicin. Gentamicin and other aminoglycoside antibiotics were effectively adsorbed from neutral aqueous solutions by the acid-extracted mycelium of M. purpurea. In addition, the acid-extracted mycelium of actinomycetes other than M. purpurea were shown to be able to adsorb gentamicin from solution.