The cannabinoid pattern of vegetable preparations from Cannabis sativa (hashish, marijuana) allows to recognize the phenotype of the plants, to be used as drug or for fiber. Cannabinoid determination by analytical point of view has represented some problems caused by the complex composition of the hexane extract. Capillary gas chromatography of the hexane extracts of vegetable samples, shows the presence of rather polar constituents that eluted, with noticeable interactions, only on polar phase. The compounds can be methylated by diazomethane and silanized (TMS) by silylating reagents. The methyl and methyl-TMS derivatives are analyzed by high resolution gas chromatography (HRGC) and by gas chromatography-mass spectrometry (GC-MS). The identification of the compounds shows their nature of cannabinoid acids, which the main by quantitative point of view results the cannabidiolic acid (CBDA). It is known that the cannabinoid acids are thermally unstable and are transformed in the corresponding cannabinoids by decarboxilation. This is of interest in forensic analysis with the aim to establish the total amount of THC in the Cannabis preparations, as the active component.