CD8+CD45RA⁺ T lymphocytes present two distinct subpopulations expressing the CD11a molecule (LFA-1 a chain) with different intensity. CD11a^dim cells represent the unprimed population within the CD8⁺CD45RA⁺ subset, whereas CD11a^bright cells are activated and may be considered as memory lymphocytes. The aim of this study was to analyze the expression of CD11a and CD18 within the CD8⁺CD45RA⁺ population in young HIV-infected individuals at different stages of disease as a marker of activation and of disease progression. Blood cells from 82 HIV-infected individuals and 23 age-matched healthy controls were stained with unconjugated CD11a, CD18, PE-goat F(ab′)₂ anti-mouse, FITC-CD45RA, and TRI-Color CD8. Quantitative analysis for three-color immunofluorescence was carried out by flow cytometry. HIV⁺ subjects were subdivided into three groups according to their CD4⁺ cell number (group A, CD4+ cells > 500/μl [20 subjects], group B, CD4⁺ cells between 500 and 200/μl [36 subjects], and group C, CD4⁺ lymphocytes < 200/μl [26 subjects]). We found a significant increase of CD11a^bright in the CD8⁺CD45RA⁺ subpopulation throughout the progression of the disease. The CD11a^bright percentage of positivity (mean) within the CD8⁺CD45RA⁺ subpopulation was 31% in healthy donors, 51% in group A, 52% in group B, and 68% in group C. CD11a^bright expression was closely related to CD18^bright (p < 0.001), but not to CD38. The relative increase of CD11a and CD18 expression in CD8⁺CD45RA⁺ T lymphocytes parallels the decrease of CD4⁺ cells and the progression of disease: an inverse correlation between the percentages of CD4⁺ cells/μl and CD8⁺CD45RA⁺CD11a^bright cells (p < 0.001) and a direct correlation between the number of CD4⁺ lymphocytes per microliter and both the number of CD8⁺CD45RA⁺CD11a^dim cells (p < 0.001) and the number of CD8⁺CD45RA⁺CD11a^bright (p = 0.002) was observed. The relative increase of CD8⁺CD45RA⁺CD11a^bright cells may represent an additional marker for monitoring HIV-induced immunodeficiency.