Breathalyzer as a method of estimating blood alcohol concentration (BAC) has been in use since 1954 when Borekenstein proved the link between increased blood alcohol concentration and traffic accidents. According to studies conducted so far, it has been proven that certain physiological parameters such as body temperature, phase of alcohol metabolism, breathing technique and others can change the concentration of alcohol in exhaled air resulting in a misjudgment of BAC. Such changes may affect the forensic classification of the intoxicated condition if it is evaluated by the breath alcohol concentration and not by the blood alcohol concentration. This study examined the association between hyperventilation and breath alcohol concentration (BrAC). The study was designed as a series of case studies and was performed on 25 healthy students whos initial BrAC and BrAC after hyperventilation for 15 and 30 sec were measured. The effect of smoking and BMI on the final result was also observed and the results were compared between male and female. The calibration accuracy of the breathalyzer test was verified by sampling venous blood and determining BAC. BrAC was statistically significantly decreased after performed hyperventilation. In this case, hyperventilation for 15 and 30 seconds caused approximately the same decrease. This study confirmed that the alcohol test as a method of determining alcohol concentration in the blood can only be used as an orientation method and not for the purpose of a definitive forensic classification of alcohol intoxication status.