The Journal of Chemical Education (JCE) recently published a letter to the editor by Dominick Labianca that was critical of methods of breath alcohol analysis because of biological variability in the blood/breath ratio (BBR) of alcohol (). His opinions deserve further comment and discussion. As background information, breath-alcohol instruments are used for two main purposes: (i) as a roadside screening test of driver sobriety and (ii) evidential quality instruments are used to generate evidence for prosecution of traffic offenders. Variations in the BBR are irrelevant in jurisdictions that enforce a statutory breath-alcohol concentration (BrAC) limit for driving, such as 0.08 g/210 L in USA. Such legislation makes it unnecessary to convert BrAC into the coexisting blood-alcohol concentration (BAC) for legal purposes. Variability in the BBR is explained by various physiological factors, such as lung function and the volume of breath discarded before a sample is captured for analysis. Moreover, BrAC is more closely related to ethanol concentration in arterial blood rather than cubital venous blood, which is the specimen used for analysis in forensic casework. In those jurisdictions that might convert BrAC into the coexisting BAC, the use of a 2100:1 BBR as a calibration factor underestimates the true venous BAC in the majority of cases.