Abstract: It has been a problem to combat the liver fluke parasite in ruminant animals such as sheep and cattle. The present invention provides antigens having specificity for the juvenile stage of the organism. They are defined as obtainable from juvenile Fasciola, preferably F. hepatica, organisms by either of two closely related methods. In both methods crude antigen is extracted from juvenile Fasciola organisms and used to raise an antiserum (by injection into rabbits for example). The antiserum is then reacted with adult Fasciola antigens. An adult antigen--adult antibody complex is formed, leaving the other components of the antiserum including juvenile specific antibodies. The juvenile specific antibodies are separated from the complex by spinning and "Millipore" filtering. This is followed either by (1) separating IgG components, including specific IgGs, e.g.