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) alpha beta + cells and CD4+ T lymphocytes were present. An abnormally high percentage of a subset of activated TCR alpha beta + cells (alpha beta + 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 gamma delta+cells, both for activated (gamma delta + DR+) and nonactivated (gamma delta + 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 renal failure.