The modulation of a polysaccharide-protein complex from Lycium barbarum (LBP3p) on the immune system in S180-bearing mice was investigated. The mice inoculated with S180 cell suspension were treated p.o. with LBP3p (5, 10 and 20 mg/kg) for 10 days. The effects of LBP3p on transplantable tumors and macrophage phagocytosis, quantitative hemolysis of sheep red blood cells (QHS), lymphocyte proliferation, the activity of cytotoxic T lymphocyte (CTL), interleukin-2 (IL-2) gene expression and lipid peroxidation were studied. LBP3p could significantly inhibit the growth of transplantable sarcoma S180 and increase macrophage phagocytosis, the form of antibody secreted by spleen cells, spleen lymphocyte proliferation, CTL activity, IL-2 mRNA expression level and reduce the lipid peroxidation in S180-bearing mice. The effect is not dose-dependent in a linear fashion. A total of 10 mg/kg dose is more effective than 5 and 20 mg/kg doses. This suggests that LBP3p at 10 mg/kg has a highly significant effect on tumor weight and improves the immune system. Copyright 2004 Elsevier B.V.