Quantitative methods of filter paper chromatography were used to analyze the amino acid content of Escherichia coli and the T (4) strain of its bacteriophage. The prepn. of bacteriophage was purified by ultra-cen-trifugation. It was hydrolyzed and treated in the same way as the bacteria. The results indicate the same amino acids are present in both the bacterial and the bacteriophage suspensions. The differences in relative amts. of amino acids in the 2 prepns. were not considered significant because of the possible impurity of the bacteriophage.