Cyclosporin A and C are new antifungal antibiotics fromTrichoderma polysporum (Link ex Pers.) Rifai. The metabolites are produced in submerged culture and are extracted therefrom by organic solvents. Cyclosporin A is a nonpolar cyclic peptide with a molecular weight of 1202.6. The cyclosporins exhibit a narrow spectrum of antifungal activity and in addition have immunosuppressive properties.