Previously, we reported an increase in the number of CD4+ T lymphocytes in the peripheral blood of smokers. In the present study, subpopulations of CD4+ T lymphocytes together with CD8+ T lymphocytes, total (CD3+) T lymphocytes, B (CD19+) lymphocytes, natural killer (CD16+) cells and total lymphocytes were examined by two-color staining using anti-2H4 (CD45RA) and anti-4B4 (CD29) monoclonal antibodies in 8 male smokers and 22 age-matched male non-smokers. The number of CD4+CD29+ T lymphocytes in smokers was significantly higher than that in non-smokers. The total number of CD4+ T lymphocytes in smokers was also significantly higher. No significant differences in CD8+ T, CD19+ B lymphocytes and CD16+ NK cells were found between smokers and non-smokers. Thus, it is suggested that the increase in the number of CD4+CD29+ (helper inducer) T lymphocytes is responsible for the increase in total CD4+ T lymphocytes in smokers.