<jats:title>Abstract</jats:title><jats:p>Pyrrolams A to D (<jats:bold>1</jats:bold>–<jats:bold>4</jats:bold>), biosynthetically new pyrrolizidinones produced by <jats:italic>Streptomyces olivaceus</jats:italic>, have been discovered by chemical screening. Their structures have been determined by spectroscopic methods and by a comparison of (<jats:italic>R</jats:italic>)‐dihydropyrrolam A (<jats:bold>5</jats:bold>) with a synthetic sample obtained from (<jats:italic>S</jats:italic>)‐proline. The pyrrolams differ from the necine bases found in plant‐originating pyrrolizidine alkaloids by their less complicated structures.