Precipitating polyclonal rabbit antiserum to bovine secretory IgA. In precipitating techniques as immunoelectrophoresis and radial immunodiffusion to identify the presence of IgA in bovine serum, milk or other body fluids or to determine its concentration. To prepare an immunoadsorbent for the purification of bovine IgA from serum or exocrine secretions. Antisera to IgA do not discriminate between serum IgA (monomeric and dimeric) and higher molecular forms as secretory IgA. This antiserum is not intended for use in non-precipitating antibody-binding or other highly sensitive assays. This does not exclude such use if proper controls are include.