The usefulness of Fungizone (the sodium desoxycholate complex of amphotericin B) in eliminating fungal and yeast contaminants from tissue cultures has been demonstrated in experiments using cell lines grown in monolayer and suspension cultures. A Fungizone concentration of 0.5 [mu]g/ml of medium inhibited growth of Aspergillus niger, Penicillium notatum, Rhizopus arrhizus, an unidentified Penicillium sp. and an unidentified Saccharomyces sp. isolated from contaminated tissue cultures, Saccharomyces cerevisiae, and Candida albicans, at inoculum levels of 100,000 mold spores, and 1,000,000 yeast cells/ml of medium. A concentration of 5 [mu]g of Fungizone/ml of serum-containing medium had little or no effect on the multiplication and morphology of L929, HeLa, a cell line derived from bovine pituitary tissue, two cell lines derived from peritoneal fluid of mice infected with Ehrlich ascites tumor, and primary cultures of chick fibroblasts. A concentration of 2.5 [mu]g/ml caused 50% inhibition of multiplication of L929 cells in Waymouth''s synthetic medium, MB 752/1.