True acid amino digestibility is main index of evaluating biological availability of feedstuffs, for which correction of the endogenous animo acids is an essential step loss.This article reviewed the measuring techniques of endogenous amino acids,and the merits and demerits of every technique were discussed.Traditionally,endogenous amino acids are determined by feeding nitrogen-free diets,the regression method or complete digestibile protein or intravenous injection AAs,but these techniques contain both des...