Emerimicins II, III and IV are new antibiotics produced by Emericellopsis microspora when 4-traps-n-propyl-L-proline (propyl proline) is added in the fermentation medium. Emerimicins are similar to antiamoebin and stilbellin. However, all emerimicins have been differentiated from the latter antibiotics by comparison of tic behavior and aminoacid composition. Propyl proline appears to induce the production of the new antibiotics since the aminoacid was not incorporated into the molecules of emerimicins II, III, or IV.