The addition of CO 2 to raw milk and dairy products controls the growth of psychrotrophic bacteria at refrigeration temperatures. The objective of this study was to determine the effects of dissolved CO 2 in milk on the performance of four important routine testing methods: antibiotic residue test, freezing point test, infrared milk component analysis, and alkaline phosphatase test. Raw or pasteurized whole milk was carbonated at <4°C to contain approximately 0 (control), 200, 400, 600, and 1000 ppm of CO 2 . The addition of CO 2 to raw milk up to 1000 ppm had no effect on the performance of the three antibiotic (β-lactams) residue tests: IDEXX SNAP, Charm II Sequential Tablet, and Delvo-P Ampule. Milk freezing point decreased linearly with increasing concentration of dissolved CO 2 , from −0.543°H (control) to −0.595°H (1000ppm). Carbonation to 1000ppm decreased milk pH (measured at 38°C) from 6.61 (control) to 6.15 (1000ppm). The effects of CO 2 on milk freezing point and pH were reversible upon removal of dissolved CO 2 . Increased CO 2 levels in milk changed the infrared absorption spectrum of milk and caused the corrected lactose readings to decrease and the corrected fat B readings to increase. For the alkaline phosphatase tests, 0 (none), 0.05, 0.1, and 0.2% raw milk were deliberately added to pasteurized milks of six levels of carbonation (0 to 1000 ppm). The addition of CO 2 did not influence the ability of Fluorophos, Charm PasLite, and Scharer Modified Rapid tests to differentiate between a pasteurized milk and a pasteurized milk with raw milk contamination.