Aims: To use ELISA and immunoblotting assays to examine the serum antibody response of cattle infected with Salmonella Typhimurium DT104 and following vaccination with Bovivac S-(R) . Methods and Results: Three hundred and twenty-nine cattle, including 16 shedding multiresistant Salmonella Typhimurium DT104, were screened for serum antibodies binding to O=1, 4, 5, 12 lipopolysaccharide (LPS) antigens before and after vaccination with Bovivac S-(R) . Sera with an ELISA reading of 0.9A (405) or above were shown to contain antibodies, of the IgG-class only, to the LPS of Salmonella Typhimurium using immunoblotting. Prior to vaccination, only 11 cattle had serum IgG-class antibodies to the O=4, 5 LPS antigens, and of these one also had antibodies to outer membrane proteins and H=i flagellar antigens. Following vaccination, 87 out of 315 cattle developed serum antibodies to the LPS of Salmonella Typhimurium. Conclusions: Evidence of infection of cattle with Salmonella Typhimurium was readily obtained with an LPS-based ELISA in association with an immunoblotting procedure, supplementing existing bacteriological procedures. This enabled the detection of an increase in the number of cattle with serum antibodies to Salmonella Typhimurium LPS following vaccination with Bovivac S-(R) . Significance and Impact of the Study: The immunoassays described provided evidence of infection with Salmonella Typhimurium and served as a valuable adjunct to established bacteriology.