Seven new cytotoxic spongian diterpenoids, dorisenones A (1), B (2), C (3), D (4), 7 alpha-hydroxyspongian-16-one (5), 15 alpha, 16 alpha-diacetoxy-11, 12 beta-epoxyspongian (6) and 7 alpha-acetoxydendrillol-3 (7) were isolated from a Japanese marine mollusk Chromodoris obsoleta (Chromodorididae), together with four known spongian diterpenoids. Their structures have been elucidated by spectroscopic evidence and single crystal X-ray analysis. Copyright (C) 1996 Elsevier Science Ltd