We have previously reported that hot-spring hydrotherapy for a short duration can change hormone levels in the blood and quantitatively as well as qualitatively regulate leukocytes and their subpopulations. In this study, we examined the effect of hot-spring hydrotherapy on the lymphocytes expressing β₂-adrenergic receptors (β₂-ARs). We obtained peripheral blood from 9 healthy volunteers (age, 49.7±11.2 years) at the same sampling time before and after (the next day) hot-spring hydrotherapy, and measured the total and differential leukocyte counts and the levels of 3 catecholamines (adrenaline, noradrenaline, and dopamine). We also analyzed the β₂-AR of lymphocyte subsets by combination with fluorescent monoclonal antibodies (CD3, CD4, CD 8, CD 19, and CD56) by using flow cytometry.
 The number of granulocytes significantly decreased after hot-spring hydrotherapy (p < 0.05). The ratio of β₂-AR⁺ CD4⁺ cells and β₂-AR⁺ CD3⁺ cells was low, but that of β₂-AR⁺ CD56⁺ cells and β₂-AR⁺ CD8⁺ cells was high. The CD8⁺ cell and CD56⁺ cell counts tended to increase after hot-spring hydrotherapy, but no significant variation was found in the β₂-AR⁺ cells of each subset. Adrenaline levels also significantly decreased after hot-spring hydrotherapy (p < 0.05). The rate of change in adrenaline levels before and after hot-spring hydrotherapy was highly correlated with the rate of change in the levels of CD56⁺, CD8⁺, and β₂-AR⁺ CD56⁺ cells. Thus, we found a difference in thepercentage of β₂-AR-expressing cells in the lymphocyte subsets. Therefore, it is possible that a short duration of hot-spring hydrotherapy decreased adrenaline levels and quantitatively influenced the natural killer cells and CD8⁺ cells, which express large amounts of β₂-AR.