The structure of a new spirobenzylisoquinoline alkaloid from Hypecoum erectum L. has been established by spectral methods and also by the x-ray structural analysis of its methiodide. It has been shown that the alkaloid, which has been called hyperectine, has a pentacyclic structure in which the tetrahydroisoquinoline fragment has the sofa conformation and the indan fragment the envelope conformation. The natural alkaloid is a mixture of the enantiomeric C-8(S), C-16(R), and C-8(R), C-16(S) forms. © 1985 Plenum Publishing Corporation.