The present studies indicate that one can dissect both the heterogeneity and functional program of the human T-cell. These investigations indicate that late in thymic ontogeny the T-cell receptor, which is involved in both antigen recognition and T-cell activation, develops. The receptor is a 90,000 mol. wt heterodimer containing constant and variable regions in its individual alpha and beta chains, which are structurally related to the immunoglobulin molecule. This structure in association with the 20/25,000 mol. wt monomorphic T3 molecule makes up the T-cell receptor complex. It is believed that these unique cell surface glycoproteins will have a critical role in controlling the immune response in man.