The two metabolites of delta9-THC are 11-hydroxy-delta9-tetrhydrocannabinol (11-OH-delta9-THC) and 11-nor-9-carboxy-delta9-tetrahydrocannabinolic (THC-COOH) acid. The detection of delta9-THC and its two metabolites was detected in antemortem and postmortem blood specimens by using gas chromatography coupled to tandem mass spectrometry in electron impact mode. The validation of this method was performed according to ISO 17025:2005. The limit of detection (LOD) and limit of quantification (LOQ) were 1 ng/ml for delta9-THC and 11-OH-THC, and 5 ng/ml for THC-COOH. The linearity of the method was within the 1-50 ng/ml range for delta9-THC and 11-OH-THC, and 5-100 ng/ml for THC-COOH. Inter-assay and intra-assay precision and relative error values were in the range of 6.8-12.3 and 7.0-15.5 percent, respectively. The analytes’ extraction recoveries were in the range of 68.7-84.1 percent. The developed method is illustrated by two examples of analyses of blood specimens collected antemortem and postmortem from toxicological practice. This method enables the reduction of biological matrix interferences, especially that originating from postmortem blood samples, which contain putrefaction products of decay and autolytical processes. Such an analytical solution makes the method more sensitive and increases the reliability of the results of toxicological analysis. 3 figures, 4 tables, and 11 references