Three new diterpenes, luteorosin [1], 12-epi-aplysillin [2], and 12-epi-12-deacetoxyaplysillin [3], have been isolated from the nudibranch mollusk Chromodoris luteorosea, along with the previously known macfarlandin A [4]. Compounds 1—4 display ichthyotoxic activity; hence, they might serve as defense allomones. © 1990, American Chemical Society. All rights reserved.