The serological response in rabbits against Listeria monocytogenes after oral or intragastric inoculation was investigated. Both the number of sero-positive animals and the average serum titres were higher in animals inoculated by the oral route. This difference was especially marked in rabbits inoculated with the lower dose (1 x 10(3) colony-forming units (cfu)), which developed a strong serological response (average serum titre of 1280 after 4 inoculations) in most of the inoculated animals (80%), without any clinical signs. The implication of these results in the epidemiology of listeriosis is discussed.