As a qualitative reference with an optimized protein content to study the normal protein composition of chimpanzee milk. To identify or quantitate a normal milk protein component using a variety of immunodiffusion techniques including immuno-electrophoresis, single and double radial immunodiffusion and electroimmunodiffusion. As a reference in nephelometry and other automated precipitation techniques. As a blocking agent or as a negative control in non-precipitating antibody-binding assays e.g. in serodiagnostic immunofluorescence and immunoenzyme tests. This normal reference does not contain assigned values for individual proteins but can be used as an internal relative standard for quantitative protein assays such as double radial immunodiffusion (Mancini, Fahey), ELISA, Western immuno-blotting and electroimmunodiffusion (Laurell), expressing the results obtained with the sample under investigation as a percentage of the protein concentration in the normal reference milk.