A new iridoid alkaloid containing a spirolactone unit, plumericidine (1), was isolated from the flowers of Plumeria rubra L. cv. Acutifolia. Its structure was elucidated by spectroscopic evidence and confirmed by X-ray diffraction crystallography. Its anticancer and antiviral activities were evaluated, but found to be insignificant. © 2009 Verlag Helvetica Chimica Acta AG.