KAWADA, E., KUBOTA, K., KURABAYASHI, H., TAMURA, K., TAMURA, J. and SHIRAKURA, T. Effects of Long-Term Running on Lymphocyte Subpopulations. Tohoku J. Exp. Med., 1992, 167 (4), 273-277-Thirteen healthy members (11 males and 2 females; mean age 19.8 years) of an athletic club underwent a long-term exercise program (five 8-km runnings per week for 40 weeks) as regular training for their club. The circulating lymphocyte number, T lymphocyte percentage, and OKT4/OKT8 ratio did not change through the 40-week training period. However, suppressor/inducer (Leu3a+Leu8+) and suppressor T cells(Leu2a+Leu15+) significantly increased. In contrast, helper (Leu3a+Leu8-) and cytotoxic T cells (Leu2a+Leu15-) significantly decreased. On the other hand, there was no change in three males (mean age 18.7 years) without the long-term exercise program. These results suggest that long-term running may induce some change in lymphocyte subpopulations.-long-term running; lymphocyte subpopulations