Biogenesis of the enantiomeric sesquiterpenes <b>1</b> and <b>5</b> of the marine nudibranch<i> Doriopsilla areolata
</i>was investigated by feeding of [1-<sup>13</sup>C]glucose, [1,2-<sup>13</sup>C<sub>2</sub>]glucose, and [1,2-<sup>13</sup>C<sub>2</sub>]acetate. Evidence is
presented that supports de novo origin of both compounds via mevalonic acid.