It has been shown that precise analysis and thorough assessment of registered physiological parameters affects the accuracy of polygraph tests used in criminal cases, external procedures or in the private sector. The polygraph shows objective parameters of various types of physiological activities of the human body during the test. A classic polygraph, by using sensors, records various parameters, such as: frequency changes and depth of breaths, blood pressure and galvanic skin reactions. The photopletysmograph, associated with the polygraph, measures changes in the volume of blood in distal blood vessels. A special cushion, placed on the testing chair, records the motive activity of the testee, monitoring their muscle tension.The following article underlines the importance of expression of emotions, including cognitive processes, physiological arguments, feelings, behavioral reactions, visible in the responses of the body of a testee on the event being the subject of the study. The aim of the test was to analyse the effect of physiology of a lie which became an exponent for interpretation and evaluation of registered physiological parameters.