The purpose of this study was to investigate the expression of lymphocyte markers in the peripheral blood of aged individuals and of young healthy blood donors. Results showed significant changes in the distribution of various T cell subpopulations. The CD3, CD4 and CD8 surface expression was not different in the elderly patients when compared to the young subjects. The number of CD4+ T cells expressing CD45 RO isoform (memory cells) was increased in aged people; CD45 RA+ CD4+ cells (naive cells) were decreased. The expression of the CD45 RB on the CD4+ cells was significantly lower in the elderly when compared to the young subjects. In contrast, the surface expression of CD45 RO and CD45 RB in the CD8+ cells was not statistically different in the young and aged subjects. The proportion of CD8+ cells coexpressing CD57 was significantly increased in the elderly subjects. These results indicate age-dependent alterations of various surface markers of T cells. These observations may be of importance in the investigation of immunoregulatory mechanisms in geriatric patients with infection, autoimmune disease or cancer.