SYNOPSIS.The free and bound amino acids of 3 strains ofTetrahymena pyriformis(variety 6) have been identified by filter paper chromatography. Twenty bound amino acids were qualitatively and quantitatively alike in each strain. The same 17 free amino acids were identified in all 3 strains; however, quantitative variations among the cultures were noted. Strain 002. an F1progeny clone obtained from a cross between strains EU 6000 and EU 6001, exhibited a combination of parental characteristics. The F1organisms resembled one parental strain, EU 6000, in the ratio of free arginine to alanine, and the other parental strain, EU 6001, in the ratio of free isoleucine to leucine. The possible genetic significance of these results is noted, and the value of chromatographic analysis as an aid to genetic study is discussed.