A simple, fast and sensitive method for the quantitative determination of strychnine residues in urine has been developed and validated. The method consists of a liquid-liquid extraction step with ethyl acetate at pH 9.2, followed by LC-MS/MS in positive atmospheric pressure chemical ionization (APCI)-mode. The method is linear in the range of 1-100 ng/mL and allows for the determination of strychnine at sub-toxicological concentrations. The accuracy of the method ranged from 1.3% to 4.4%. The method was used to determine the excretion profile of strychnine after the ingestion of an over-the-counter herbal preparation of Strychnos nux-vomica. Each volunteer ingested a dose equivalent to 380 micro g of strychnine. This dose is lower than the prescription dose but results in the detection of strychnine for over 24-h post administration. Maximum detected urinary concentrations ranged from 22.6 to 176 ng/mL. The results of this study show that the use of this type of preparation by athletes can lead to a positive doping case.