The isolation and determination, by spectroscopic analyses and chemical correlation, of the structure and stereochemistry of (+)-epimaritidine, a new alkaloid from Zephyranthes rosea, is reported. A facile transformation of maritidine to (+)-epimaritidine is described and the mechanism is appraised in the light of the thermodynamic stability of the latter epimer. (+)-Epimaritidine comprises a missing link in the C-3 epimeric pairs of 5,10b-ethanophenanthridine alkaloids of the vittatine-haemanthamine type. © 1985.