<jats:p><jats:bold>Novel Cyclosporins from <jats:italic>Tolypocladium inflatum</jats:italic>. The Cyclosporins K–Z</jats:bold><jats:p>The fungus <jats:italic>T. inflatum</jats:italic> produces a plethora of oligopeptides, the cyclosporins, which exhibit remarkable biological activities. Cyclosporin A, the main metabolite, represents a potent immunosuppressant which opened new ways in the immunotherapy of bone marrow and organ transplantations. In addition to the already described cyclosporins A–I, we report now the isolation of the cyclosporins K–Z. The structural assignments of these novel congeners are based on chemical degradation, correlation reactions, mass spectra, and extensive analysis of <jats:sup>1</jats:sup>H‐ and <jats:sup>13</jats:sup>C‐NMR spectra. All cyclosporins are cyclic undecapeptides differing from each other by minor variations in the amino‐acid sequence. Comparison of the immunosuppressive and antifungal effects furnished new information concerning structure‐activity relationships.