The losses of amino acid during acid hydrolysis of oviduct magnum protein from the domestic fowl have been measured using a Technicon TSM-1 amino acid analyser. The results were subjected to statistical analysis and a linear regression was obtained for each amino acid investigated. Methionine, in the presence of oxygen, did not exhibit significant degradation. A loss of 5.5% was found for phenylalanine after 24 h of hydrolysis under nitrogen. It is suggested that the results could be applied to animal proteins from tissue of similar composition but not to analysis of protein from plant materials.