Twenty-seven cord blood samples from healthy newborns were processed according to a "whole blood" flow cytometric analysis. The CD3-positive T cells were a variable subpopulation representing 44.8 +/- 13.3% of lymphocytes. The majority of the CD3+ cells are CD38+. Newborn T cells have lower levels of both IL-2 receptors and HLA-DR than do adult T cells. The CD4-positive T cells represented 31.0 +/- 10.8% of lymphocytes with a great prevalence of the CD4+/CD45RA+ population. The CD3+/CD8+/CD11b+ cells are increased to 23.4 +/- 7.1% of lymphocytes. The CD57 antigen is not expressed. The NK population, CD16+/CD56+, is increased to 25 +/- 11% of lymphocytes. Of CD19+ cord blood B lymphocytes 68% coexpressed CD5. Thus "suppressive" and "naive" cells are prominently represented in cord blood.