Strychnine is an alkaloid of great toxicity. The minimum lethal dose is about 50 to 100 mg for adults after the ingestion. It was largely used as a therapeutic agent and as a rodenticide for a long time. Since 1974, it is not commercialized in Portugal. Two fatal cases and a clinical case were only reported by Toxicological Laboratory of the Institute of Legal Medicine of Coimbra from 1960 to 1995.This paper describes the analytical method for strychnine determination in biological samples by GC/MS and their application in the investigation of the two cases involving ingestion of strychnine: a suicidal case and a clinical one. The procedure extraction was performed with toluene: n-heptane: isoamyl alcohol under basic conditions and the procedure purification with a acid solution. In the quantification of strychnine, the papaverine was used as internal standard. The limit of detection was 0.1 μg/g or 0.1 μg/ml in the analyzed specimens such as blood, urine, liver, kidney, lung and heart. The recoveries at different concentration levels ranged from 81.2 to 98.7% in the various specimens. The variation coefficients were, in general, under 10%. In the fatal case the strychnine levels in blood, liver, kidney, hear, lung, small intestine, and stomach contents ranged from 3.3 to 281.5 μg/ml or μg/g. In the clinical case the concentrations in blood, urine and stomach contents were 0.35; 15.3; 0.01 μg/ml, respectively.The results of the toxicological analysis are in agreement with those in the scientific literature. The clinical case manifested typical symptoms of strychnine intoxication and in the fatal case no specific lesions were found during the autopsy except oedema of the viscera.