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