Four murine monoclonal antibodies (MAbs)to Salmonella typhi flagellin were produced. These MAbs did not react with eight other enterobacterial strains tested: Salmonella enteritidis, Salmonella typhimurium, Salmonella paratyphi A, Escherichia coli, Shigella flexneri, Shigella sonnei, Yersinia enterocolitica, and Campylobacter jejuni. Allfour MAbscross-reactedwith Salmonella muenchen flagellin indicating specificityfor d antigenic flagellar epitope. One MAb(C4) was selected to developa double antibody sandwich enzyme-linked immunosorbent assay (ELISA) to detect S. typhi flagellin in serum samples. By use of this assay S. typhi flagellar antigen was detected in 95.5% of serum samples from patients with positive hemoculture for S. typhi, in 93.6% of samples from patients with positive serodiagnosis of typhoid fever, in 26% of samples collected from patients who were initially hemoculture-positive for S. typhi and who had undergone 7–8 d of chemotherapy, in 8.5% of samples from healthy persons from an endemic area, and in no samples from healthy persons from a nonendemic area. The presence of high levelsof flagellin antibody titers did not interfere with the antigen detection. The detection of S. typhi flagellar antigen in patient serum may have practical value for rapid diagnosis of typhoid fever.