In this test were verify the possibility of the influence of windshield washer fluid containing ethanol on an alcohol breath test. The premise was that anti-freeze washer fluids used in automobiles contain ethanol, and that the use of such fluids results in ethanol vapour permeating the automobile's cabin. Tests were carried out on individuals seated on the front seats of an enclosed automobile cabin. Five different types of anti-freeze washer fluids suited for temperatures between -19 degrees C to -35 degrees C commonly available at a range of different petrol station chains throughout the Czech Republic were used. In total 34 measurements were taken. Not even in one instance could a measurement of zero be obtained within 60 seconds to 4 minutes of the use of ethanol-based washer fluid. The longest positive test lasted for 13 minutes. The highest measured value was 0.71% per hundred. Immediately after exiting the automobile and taking several breaths of fresh outside air tests were negative in all cases. All tests subjects described a clear odour of windscreen washer fluid in the cabin in all instances, which was evident even after breathalyzer tests showed zero values. It is hence verified that using ethanol-based windscreen washer fluid which is commonly accessible on our market to spray the windscreen can skew the results of breathalyzer tests in the sense of generating false positives. Due to the characteristic odour described, drivers should themselves be aware that any test undertaken could not be in his or her favour. To eliminate the apparent presence of alcohol, it is however enough to exit the cabin and to take several (2-3) breaths of fresh air to absolutely guarantee a fair test. A positive test at this stage points to a different underlying reason than ethanol-based windscreen washer fluid being used.