The target of this study was to compare the results of breath analysers and "lege artis" laboratory blood examinations when determining alcohol levels. This was then used to determine whether any differences exist between the two methods, and how large these differences are. 610 cases from 11 workplaces in the Czech Republic and Slovakia were analysed. The type of breath analyser was not taken into consideration. All cases had to be in the elimination phase. Difference of time between breath test and blood test were rectified through the use of reverse recomputation. It was detected that only 20.8% of the results of respiratory analyser tests correspond to the detected real alcohol level in blood. The maximum difference when a respiratory analyser measured more than a blood test was 1.34 g x kg(-1). and the maximum difference when the analyse measured less was 1.86 g x kg(-1).