Evidential breath alcohol analyzers intended for police use in Canada must undergo an evaluation process to determine whether they meet the Standards for Approved Instruments of the Canadian Society of Forensic Science (CSFS) Alcohol Test Committee (ATC). The MKIII Dual C uses two detectors: infrared and an electrochemical sensor. Vapors from aqueous acetone solutions of 5, 10, and 50 milligrams in 100 milliliters of solution did not produce any readings other than zero on the instrument. Vapors from aqueous solutions of acetaldehyde, methanol, isopropanol, toluene, ethyl acetate, and diethyl ether were blown into the MKIII Dual C to determine potential interference with the operation of the instrument. The instrument registered an interference result with acetaldehyde, methanol, isopropanol, ethyl acetate, and diethyl either while toluene registered as a zero reading. Results show that the MKIII Dual C met the ATC standard for accuracy and precision when measured against simulated breath alcohol vapors. Both the precision and accuracy were well within the standards for acceptance throughout the range of simulator alcohol concentrations tested. The human subject testing demonstrated confidence intervals well within the ATC criteria when compared to two Approved Instruments. The MKIII Dual C is able to distinguish other potentially interfering substances from ethanol and able to detect ambient air contamination that might contribute to an apparent blood alcohol concentration. The MKIII Dual C maintained its initial calibration throughout the evaluation, a period of approximately 5 months. No mechanical or electrical problems were encountered and the instrument performed without breakdown. 3 tables, 5 references