Cannabis has been known as a medicine for several thousand years across many cultures and its beneficial effects are mostly due to the presence of cannabinoids, unique natural products, whose pharmacology is going to gain increasing interest in the scientific community. The discovery of the main psychoactive constituent of Cannabis sativa L., Delta^sup 9^-tetrahydrocannabinol (Delta^sup 9^-THC), led to the identification of at least 100 additional phytocannabinoids, including cannabidiol (CBD), cannabidivarin (CBDV), Delta^sup 9^-tetrahydrocannabivarin (Delta^sup 9^-THCV), and cannabigerol (CBG). These molecules are gaining growing interest for their medical properties; however, further research is needed to assess the differences in their pharmacokinetic and pharmacodymanic profiles. The aim of this study was to set up a rapid and accurate method, by using the LC-MS-IT-TOF technology, to detect and quantify CBD, CBDV, Delta^sup 9^-THCV, and CBG in biological matrices. Data show that the method developed here is linear in the calibration range; recoveries from mouse tissues were in the 50-60% range and sensitivity was 2 ng/mL for CBDV, 4 ng/mL for CBG and THCV, and 7 ng/mL for CBD. The method is rapid, precise and accurate, and it will represent a fundamental tool to evaluate the pharmacokinetic and pharmacodynamic properties of selected phytocannabinoids in tissues from different animal models, and develop new cannabinoid-based medicine.