After reaction with nitric acid, brucine can be transformed into cacotheline, and then measured indirectly by adsorptive stripping voltammetry. This method is based on the adsorptive accumulation of cacotheline at a hanging mercury drop electrode, followed by cathodic linear sweep voltammetry. The cathodic peak potential is about -0.35 V (vs. saturated Ag/AgCl). The detection limit of 2.0 10 - 9 M is obtained under optimized conditions. The electrochemical behaviour of cacotheline and the mechanism of the electrode reactions are discussed.