AIM: To investigate the immunoregulatory effects of cinobufagin from the chloroform extract of Venenum Bufonis, a famous traditional Chinese medicine in vitro. METHODS: Proliferation of the splenic lymphocytes in Balb/c mice was measured by MTT assay. The metaboilic level and phagotrophic activity of PMΦ were also determined by MTT assay. The expressions of CD4 and CD8 and cell cycle of the splenic lymphocytes were detected by flow cytometry. RESULTS: Administration of cinobufagin or coadministration with Con A or LPS increased the cell proliferation and the percentage of S phase cells in the splenic lymphocytes at a dose-dependent manner(P<0.05 or P<0.01). Cinobufagin also enhanced the metabolic capability of MTT and the phagocytosis function of PMΦ(P<0.05 or P<0.01). In addition, it was found that the single administration of cinobufagin or coadministration with Con A or LPS also could increase expressions of CD4 and CD8 in T lymphocytes(P<0.05 or P<0.01). CONCLUSION: Single administration of cinobufagin or coadministration with Con A or LPS could enhance the reactive ability to the splenic lymphocytes and PMΦ in mice. The data indicate that the immunoregulatory effect of cinobufagin is related to the increased expression of CD4+ and CD8+ in DP (double positive) phenotype and S phase cells of T lymphocytes. AIM: To investigate the immunoregulatory effects of cinobufagin from the chloroform extract of Venenum Bufonis, a famous traditional medicine in vitro. METHODS: Proliferation of the splenic lymphocytes in Balb/c mice was measured by MTT assay. The metaboilic level and phagotrophic activity of PMΦ were also determined by MTT assay. The expressions of CD4 and CD8 and cell cycle of the splenic lymphocytes were detected by flow cytometry. RESULTS: Administration of cinobufagin or coadministration with Con A or LPS increased the cell proliferation and the percentage of S phase cells In the splenic lymphocytes at a dose-dependent manner (P<0.05 or P<0.01). Cinobufagin also enhanced the metabolic capability of MTT and the phagocytosis function of PMΦ (P<0.05 or P<0.01). In addition, it was found That the single administration of cinobufagin or coadministration with Con A or LPS also could increase expressions of CD4 and CD8 in T lymphocytes (P<0.05 or P<0.01). CONCLUSION: Single admini The data indicates that the immunoregulatory effect of cinobufagin is related to the increased expression of CD4+ and CD8+ in DP (double positive) phenotype. And S phase cells of T lymphocytes.