Wastewater treatment plant workers are exposed to microbes, including Salmonella, but the prevalence of antibodies against Salmonella species or serovars in their serum samples has not been studied. Antibodies against Salmonella Infantis and lipopolysaccharide antigen common to S. Enteritidis and S. Typhimurium in immunoglobulin classes IgA, IgM and IgG were measured from 79 serum samples of wastewater treatment plant workers and from 79 blood donor samples. Faecal samples for Salmonella and Campylobacter were studied. Gastrointestinal, dermal and other symptoms were compared between 81 wastewater treatment plant workers and 89 food-processing workers. The blood donors had more antibodies against all of the tested antigens expect for S. Infantis in IgM and IgA classes, even though the wastewater treatment plant workers had more gastrointestinal symptoms than the controls. No Salmonella or Campylobacter were found in any faecal samples. Salmonella is not a probable cause of symptoms among wastewater treatment plant workers.