This paper reports the results of an interlaboratory study of quantitative amino acid determinations in different protein hydrolysates. 21 laboratories participated in the test using three chromatographic techniques: IEC (15), RP-HPLC (8 with 2 variants) and GC (1). To evaluate the matrix effect on the analysis, four types of samples were considered: an amino acid standard solution, a milk protein concentrate, a mixture of cereals and milk products and a feed sample. The results of determination of the twenty amino acids (including sulphur-containing amino acids and tryptophane after different hydrolyses) are expressed in g/kg dry matter. They were evaluated according to ISO standard 5725. This test shows the advantages and disadvantages of the different methods applied: IEC is more precise (r and R) than HPLC. The values obtained by IEC and HPLC are in agreement for all amino acids except Cystine. The matrix of the analysed samples plays a great role (hydrolysis). The best r and R values were obtained with the standard solution, the worst with the feed sample
