The appearance of potentially counterfeit "Colgate" toothpaste on the American market prompted a criminal investigation by the United States Food and Drug Administration (FDA), including the collection of c. 60,000 tubes of toothpaste from retail outlets and product distributors. Microbiological testing was performed based on the FDA Bacteriological Analytical Manual, which determined the presence and number of bacteria present in the products. Bacteria were isolated from each "Colgate" variety; up to 2 106 cfu/g were isolated from some of the product units. Using conventional microscopic and biochemical bacterial identification methods, most of the bacteria isolated from these samples were Gram-negative rods of several genera, including Pseudomonas, Serratia, and Klebsiella. Most of the organisms isolated represent opportunistic pathogens, and therefore, counterfeit "Colgate" toothpaste containing high levels of bacteria pose a human health hazard. Abstract published by arrangement with John Wiley & Sons.