<jats:p>From a strain of <jats:italic>Aspergillus nidulans var. echinulatus</jats:italic>, A 32204, echinocandin, a novel polypeptide antibiotic complex with high and specific anti‐yeast activity was isolated. The main component, echinocandin B, was separated by counter‐current distribution. A tentative molecular formula C<jats:sub>52</jats:sub>H<jats:sub>81</jats:sub>N<jats:sub>7</jats:sub>O<jats:sub>18</jats:sub> is discussed. The antibiotic is characterized by its IR. and NMR. spectra and by its characteristic hydrolytic degradation products: linoilic acid, <jats:sc>L</jats:sc>‐4‐hydroxyproline, <jats:sc>L</jats:sc>‐4‐oxoproline, (2<jats:italic>S</jats:italic>, 3<jats:italic>S</jats:italic>, 4<jats:italic>S</jats:italic>)‐4‐methyl‐3‐hydroxy‐proline, <jats:sc>L</jats:sc>‐threonine (2 mols), and 1‐(<jats:italic>p</jats:italic>‐hydroxyphenyl)‐3‐amino‐propan‐2‐one.