To investigate effect of water extract of PaIMuITang(PMT) on human cancer cell-lines and immunocytes, this research estimated proliferation of A431 cell line, KHOS-NP cell line, mouse thymocytes and mouse splenocytes, Nitric Oxide(NO) from macrophage, apoptosis and subpopulation of the mouse thymocytes. The results were obtained as follows; 1. PMT inhibited the. proliferation of A431 cell line, but it is not significant. 2. PMT inhibited the proliferation of KHOS-NP cell line, but it is not significant. 3. PMT stimulated the proliferation of mouse thymocytes, being compared Con A non-treated group. 4. PMT stimulated the proliferation of mouse splenocytes, being compared LPS treated group. 5. PMT l00g/mQ inhibited the production of NO from macrophages in vitro, being compared NPS IFN treated group. 6. PMT inhibited the production of NO from macrophages in vivo, being compared LPS|IFN treated group. 7. PMT accelerated the induction of apoptosis of the mouse thymocytes. 8. In subpopulation PMT decreased $T_H$ of the mouse thymocytes, but increased T /dT s of the mouse thymocytes.