A novel apoptosis inhibitor, dykellic acid (1), was isolated from the fermentation broth of Westerdykella multispora F50733. The structure of 1 was elucidated by spectral and X-ray crystallographic data. Compound 1 inhibited the etoposide-induced apoptosis of human monocytic leukemia U937 cells. (C) 1999 Elsevier Science Ltd. All rights reserved.