Immunohistochemistry was performed to investigate the localization of CsTegu20.6 within the adult worm. Fresh-washed adult worms of C. sinensis were fixed with 4% paraformaldehyde, dehydrated by a graded ethanol series and embedded in paraffin blocks. Sections of adult fluke (4 μm thick) were mounted on glass slides, deparaffinized, rehydrated and washed in phosphate-buffered saline (PBS). The slides were incubated with anti-CsTegu20.6 sera diluted 1:100 in PBS at room temperature for 2 h and washed several times in PBS. Non-immunized rat sera were employed as a negative control. The slides were then incubated for 2 h in FITC-conjugated anti-rat IgG (1:200 dilution, Sigma, St. Louis, MO, USA). All specimens were washed and examined using a light/fluorescence microscope (Axioplot, Carl Zeiss, Jena, Germany).