The European Union drew attention to the increased consumption and the reports of adverse reactions to caffeine in recent years. The EU Commission in Regulation No. 536/2013 dated 11 June 2013 expressed concern about the caffeine content in the products. It is important to develop a simple and accurate methods for determining the level of caffeine in the biological material for accurate exposure assessment, as well as in the caffeinated products. The use of saliva as a diagnostic material is painless, non-invasive and does not require the participation of professional medical personnel. The compounds identified in saliva showed relatively high durability. The developed method for the determination of caffeine by high performance liquid chromatography with diode array detection (HPLC-DAD) after extraction of caffeine from saliva by solid phase extraction (SPE) is characterized by the linearity in the concentration range 50 - 2000 ng/mL. This method have low detection (12 ng/mL) and quantification (40 ng/mL) limits and high intra-day (4.87% for low concentration and 2.10% for high concentration) and inter-day (5.84% for low concentration and 2.43% for high concentration) repeatability.