AFTER our initial observation in 1978 of engraftment of nonfunctional intrauterine-derived maternal T cells in a patient with severe combined immunodeficiency without graft-versus-host disease,^{1 , 2} we prospectively examined all new patients with severe combined immunodeficiency for the presence of such engrafted cells in order to determine the incidence of this phenomenon. Peripheral lymphocytes were separated into E-rosette-positive and E-rosette-negative populations and then typed separately for HLA. HLA-DR antigens and other lymphocyte markers on both the E-rosette-positive and negative cells were also determined. Of 16 patients examined, four were determined to have E-rosette-positive maternal lymphocytes. The engrafted cells were functionally inactive during . . .