ABSTRACTThis is a study of the effectiveness of the built-in acetone correction procedure, in measuring blood alcohol concentrations, using the Intoxilyzer® 5000C. Measurements of headspace vapours of alcohol standards and alcohol-acetone mixed standards delivered from simulators were taken using Intoxilyzer® 5000C. The alcohol concentrations in the aqueous solutions used were such that the target value of headspace vapour would be 0, 50, 100, 150 and 200 milligrams (mg) of alcohol/100 millilitres (mL) of solution. Acetone concentrations in the solutions were 0, 1, 3, 5, 10, 25, 32, 34, 35, 40, 100 and 500 mg/100 mL. Measurements were repeated 15 times and the error message (“INTERFERENT” or “INVALID SAMPLE”), if any, was noted in each case. The “INTERFERENT” message consistently appeared above the calibration level, 35 mg/100 mL of acetone in the solution. Even when the “INTERFERENT” message appeared, the headspace alcohol concentration measured was accurate within ± 10 mg/100 mL. The Intoxilyzer® 5000C yields accurate blood alcohol measurements in the presence of acetone up to 100 mg/100mL.