The specific immune response of unripened fruits and ripened fruits of Rubus coreanus Miquel was examined in BALB/C mice. The 70% ethyl alcohol extracts (20 or 100 mg/kg) of unripened fruits (RCE-I) and of ripened fruits (RCE-II) were administered p.o. once a day for 7 days. RCE-I and RCE-II decreased the viability of thymocytes, but increased the viability of splenocytes. Also, RCE-I enhanced the population of helper T and cytotoxic T cells in thymocytes and RCE-II enhanced the population of helper T cells. Furthermore, RCE-I and RCE-II decreased the population of B220⁺ cells and Thy1⁺ cells and helper T cells in splenocytes. In a general way, the immunosuppressive action of RCE-I was more potent than those of RCE-II. These results suggest that RCE-I and RCE-II have a regulative action of immune response via decrease the viability of thymocytes and increase the viability of splenocytes.