Immune cell subsets, when measured by two-color flow cytometry in a population of 129 hemodialysis patients, showed significant variance from normal values. Lymphopenia, decreased absolute counts, and altered percentage values of immune cells were found. Increased proportions of CD3+, T cell receptor (TCR) αβ+ cells and CD4+ T lymphocytes were present. An abnormally high percentage of a subset of activated TCR αβ+ cells (αβ+ DR+) was also seen in hemodialysis patients. The proportion of B lymphocytes was found to be significantly lower as compared with controls. Relative values for TCR γδ+ cells, both for activated (γδ+ DR+) and nonactivated (γδ+ DR-) subsets, as well as for CD8+ lymphocytes and natural killer cells did not vary from those of normal controls. Also, the CD4+/CD8+ ratio showed no significant change. Analysis of absolute counts of the investigated immune cell populations revealed significantly decreased numbers for the majority of subsets, as a result of the preexisting lymphocytopenia, characteristic of end-stage renal disease. We conclude that profound quantitative alterations of immune cells, including TCR+ T cells subsets, exist in hemodialysis patients. These account, at least in part, for the immune dysregulation associated with chronic re