SummaryThe antigenicity of the biosynthetically labelled somatic and excretory/secretory proteins of adultFasciola hepaticawas investigated over 20 weeks of an infection withF. hepaticain sheep. The antibody response was initially detected by 6LISA 2 weeks after infection, and was sustained at this level for the remainder of the infection. Immunoprecipitation analysis indicated that a large number of proteins were recognized by the sheep, with several dominant antigens occurring in the 29‐31 kilodalton molecular weight range. No differences were found between the antigens recognized by sheep in the early or late stages of infection suggesting that there are similarities between the antigens of the immature and mature forms of the parasit