The purpose of this research was to investigate the effects of Insamyangyoung-tang water extract (IYT) on the specific immune response in BALB/c mice. When IYT (500mg/kg) was administerd p.o. once a day for 7 days to BALB/c mice, the cell viability of thymocytes and splenocytes was increased. Also, IYT increased the population of CD4⁺ cells in thymocytes and the population of Thy1⁺ cells and CD4⁺ cells in splenocytes. In addition, IYT increased the production of γ -interferon and interleukin-2 from thymocytes and the production of γ -interferon from splenocytes. These results suggest that IYT enhances the specific immune response via activation of Th1 cells in thymocytes and splenocytes.