The isolation and structural elucidation of a new antileukemic iridoid lactone, allamandin (I), and the new companion iridoids, allamandicin (3) and allamdin (4), are reported. Elemental analysis and mass spectrometry established a C15H1607 molecular formula for allamandin (l), and the structure was established by spectral studies and dehydration to the previously known and cooccurring plumericin (5). Assignment of configuration was effected by spin-decoupling studies of acetylallamandin (2). The isomeric iridoid, allamandicin (3), was characterized by dehydration to plumericin (5) and additional chemical and spectral studies. The structure of allamdin (4) was deduced by spectral studies, and proven by direct X-ray crystallographic analysis.