Herbimycin C is a minor analogue of the herbimycin complex isolated from Streptomyces hygroscopicus. Herbimycin C possesses potent antitumor activity and converts Rous sarcoma virus-infected rat kidney cells into normal cells. Until now limited access has restricted a full investigation of the properties of herbimycin C. Research on related metabolites, herbimycin A and geldanamycin, has stimulated intensive interest in this class as selective antitumor agents and for prolonging the viability of tissue-cultured cells and organs.