Degradative schemes are reported for the alkaloids hasubanonine (1) and protostephanine (2) of Stephania japonica to allow labelling patterns to be determined. Acetolysis of (1) leads eventually to a phenanthrene (5c) by removal of the ethanamine bridge. N-Methylation and Hofmann elimination of (2) gives one major olefinic product, assigned structure (6a) from 1H n.m.r. data and confirmed by synthesis of specifically 13C-labelled material.