1. 1. The distribution of nitrogen in five tissue fractions of M. expansa, T. actinioides, and C. perplexa has been determined. M. expansa and T. actinioides are distinct with respect to the amount of nitrogen in these fractions. T. actinioides and C. perplexa are closely related with regard to these nitrogen determinations. 2. 2. The amino acids of the non-protein and protein fractions of M. expansa, T. actinioides, and C. perplexa were determined qualitatively by paper chromatography on buffered papers. Nineteen amino acids were identified as common to the protein fractions of all three species. From seventeen to twenty-two amino acids were identified in the non-protein fractions of these cestodes. Certain qualitative differences between species were found in this fraction. This is the first report of β-alanine, β-aminoisobutyric acid, and γ-aminobutyric acid in cestodes. The possible roles of these amino acids in the metabolism of tapeworms is discussed. 3. 3. The amino acids present in sheep bile which are available to T. actinioides were determined. Bile as an environment for parasitic helminths is discussed as well as its contribution to the intestinal environment.