All L. monocytogenes-positive samples and a cross section of Listeria-negative samples were selected. A total of 1883 samples were tested for lactate and acetate. Samples represented different categories of processed meats and poultry products including uncured and cured poultry products and pork and beef products that were sliced at retail deli or pre-packaged in USDA- or stateinspected plants. Some samples were categorized as mixed products since they were prepared from a mixture of beef, pork and/or poultry. Samples were obtained from four states (California, Georgia, Minnesota, and Tennessee) participating in FoodNet and PulseNet and representing geographic diversity in the U.S.