The experiments outlined in this proposal are designed to establish if the portion integrated into the membrane (core) of two thymocyte differentiation alloantigens, Thy-I and TLA (leukemia Antigens) are similar or distinctly different. In addition alteration in these molecular parts, due to malignant transformation, will be determined by isolating the core peptides from normal and malignant cells. To make deductions as to similarities existing between these molecules, the isolated cores will be analyzed by amino acid analysis, peptide maps, molecular weights and if sufficient quantities can be isolated by limited N-terminal sequence analysis.