In the presented paper a retrospective analysis of the presence of anti-Salmonella enteritidis and Salmonella typhimurium (done in years 2004-2006) antibodies on the cohort of 2500 sera from patients hospitalized and consultated in the Institute of Rheumatology have been done. In a high sensitive ELISA method, a commercially available LPS from above mentioned Salmonella species – as antigen showing the highest frequency of appearance in Polish population and because of that diagnosed as an etiological, was factor in unclassified arthritis, used as antigen. Also, usefulness of these methods for serodiagnostic, have been done considering their cross-reactivity with other bacterial species like Yersinia enterocolitica O3, Borrelia burgdorferi and Chlamydia trachomatis, which are objects of interesting for (with exception of Ch. trachomatis) physicians especially from Pediatric Clinic (about 50% of estimations was commissioned children and teenagers). Percentages of positive results for presence of antibodies against S. enteritidis and S. typhimurium, independently of Ig-s clases, were this same range like in the healthy population, what means, that these results can be taken under consideration only as a particular cases – basing on anamnestic interview and deep clinical analysis. A retrospective analysis of antibodies levels and class showed evident differences between these two Salmonella species (S. enteritidis – prevalence of antibodies IgG class, and S. typhimurium – prevalence of IgA and IgM class antibodies). A high frequency of cross-reactivity (about 43%) of antibodies against both S. typhimurium and Y. enterocolitica O3 and for „taxons” like for example B. burgdorferi or Ch. trachomatis may be (in part) explanated by similarity of external part of bacterial cell wall, but we have to considered also co-infection or manifestation-loss infection with going involvements. We strongly suggest, that presence of antibodies should be confirmed by specific method like inhibition ELISA and Western-blotting.