The purpose of the study was to test in experimental mouse model if some immunological parameters could be helpful in recognizing Listeria infections. Delayed type hypersensitivity (DTH) and ELISA tests carried out with soluble fractions of L. innocua (serotype 6a) or L. monocytogenes (serotype 4b) seem to be useful in detecting listeriosis at an early stage. Although crude antigen fractions were used in this study, very weak only nonspecific DTH reactions were observed in unifected animals and they could be easily distinguished from the DTH reactions developed by the animals infected with Listeria. However, genetic factors influenced specific anti-listerial reactivity and it was especially observed when DTH test was used as an indicator of Listeria infection. In contrast to DTH and ELISA tests, determination of antibodies active in agglutination or passive haemagglutination assay seem useless in detecting listeriosis at an early stage of infection.