The reactivity of the antiserum is restricted to salivary amylase. In immunoelectrophoresis and radial immunodiffusion, using various antiserum concentrations against human saliva a single precipitin line is obtained and shows a reaction of full identity with the purified immunogen. No reaction is obtained with human plasma. In precipitating techniques as immunoelectrophoresis and single and double radial immunodiffusion (Mancini, Ouchterlony) to identify the presence of salivary amylase or to determine its concentration. The presence of non-precipitating antibodies has not been assayed. This does not exclude the use of the antiserum in non-precipitating antibodybinding techniques if proper controls are included.