It is reported that changes in immunological system are one of the underlining mechanisms of balneotherapy effects. Since there is no study concerning the mechanisms how balneotherapy with a simple thermals works, we tried to examine both the changes of immunological functions and stress relieving effect of balneotherapy. Fourteen inpatients (mean age 63 years) suffering from such as cerebrovascular diseases participated in the present study. Before and after 6-week balneotherapy, lymphocyte subset counts, levels of cytokines (IL-4, IL-6, IF-γ etc.) were determined and lymphocyte blastogenetic tests were also performed. In addition, stress barometers (urinary 17-ketosteroidsulfate (17KSS)/17hydroxycorticosteroid (17OHCS)) were measured. As a result, no significant changes in cytokine levels were observed. Percentage of T cell count decreased and that of B cell increased. Percentage of suppressor T cell count decreased and that of helper and killer T cell tended to increase (not significant). Lymphocyte blastogenetic tests by ConA and PWM showed enhanced responses and urinary 17KSS/17OHCS levels increased after balneotherapy. From these findings, it is suggested that 6-week balneotherapy with a simple thermals has a potential of augmenting immunological functions and also possesses stress relieving effect.