The immunodiagnosis of human infections with Fasciola hepatica using purified parasite cysteine proteinases as antigens is reported in this paper. IgG enzyme-linked immunosorbent assays (ELISAs) with 2 cysteine proteinases of 26 kDa (Fas1) and 25 kDa (Fas2), obtained from the regurgitated material of adult worms, were evaluated with serum samples from 38 patients infected with F. hepatica, from 54 patients with other parasitic infections and from 46 healthy volunteers. The diagnostic sensitivities for detection of F. hepatica infection at a serum dilution of 1 in 500 were 89% and 95% with Fas1 and Fas2 respectively. The specificity of the ELISAs was 98% for Fas1 and 100% for Fas2. IgG ELISA with Fas2 is a highly sensitive and specific assay for the immunodiagnosis of human fascioliasis.