A new compound was isolated from the reaction mixture after O-demethylation of 6-O-acetyl-10 alpha-acetoxycodeine with boron tribromide. The structure of this compound, 10 alpha-hydroxy-beta-isomorphine, was elucidated by spectral data, and its spatial arrangement was deduced from an NOE experiment. Capillary zone electrophoresis was used for separation of morphine and its 10-hydroxy analogues.