Infections with Listeria monocytogenes have been increasing in incidence over the last decade. Listeria species are found widely in the environment, frequently isolated from the soil, water, sewage, and from a variety of wild and domestic animals. Outbreaks of human listeriosis have been linked to contaminated coleslaw, milk, and other dairy products. Since Listeria is an intracellular pathogen, it is not surprising that the majority of symptomatic cases have occurred in individuals receiving immunosup pressive therapy, or with some defect in their cell-mediated immune system.