Glycyrrhizin (GL), a plant extract, has been evaluated for its inhibitory effect on HIV replication in vitro and for its improvement of clinical symptoms in HIV-infected patients. In this study, we used GL in a murine AIDS model (MAIDS) to evaluate these effects. C57BL/6 mice were inoculated with LP-BM5 murine leukemia virus to cause MAIDS. Treatment with GL supplemented with glycine and cysteine (Stronger Neo-Minophagen C, SNMC) was then begun on day 0 or 4 wks after virus inoculation. SNMC was administered three times a week for up to 19 wks. Immunological abnormalities were monitored with respect to the surface phenotype identified by two-color staining for CD3 and IL-2 receptor beta-chain. All mice infected with the virus alone developed MAIDS and died by 14 wks after infection. The immunopathogenesis was estimated to be an abnormal expansion of intermediate CD3 cells (i.e., extrathymic T cells) as well as other types of lymphocytes. SNMC did not change the total mortality rate. However, some mice that began the treatment on day 0 or 4 wks after infection survived 3 wks longer. Splenomegaly and lymphadenopathy in such mice were suppressed. These mice showed normal phenotypic features and normal responses to Con A. These results suggest that SNMC is effective in some MAIDS mice in preventing the progression of disease. When lymphocytes isolated from the liver, spleen and lymph nodes of diseased mice were cultured in vitro, they showed a spontaneous proliferation. Interestingly, such proliferation was inhibited by addition of liver lymphocytes, but not splenic lymphocytes, obtained from normal or SNMC-treated mice. Since liver lymphocytes contains intermediate CD3 cells with autoreactivity, they may possibly suppress the progression of disease.