AIM:To observe the effects of a chemically synthesized tetrose and a natural yeast mannan on experimental liver metastasis of mouse melanoma.METHODS: After treated with 4mg tetrose (tetrose group) or 4mg mannan (mannan group) for 30 minutes at 37&mgr;,0.5ml 1 10(6) B16-MBK melanoma cells were injected into the spleen of mice.Fifty-five days later, melanoma metastatic nodes on the surface of the liver and in other organs as well as mouse survival time were observed.RESULTS: Of the 6 mice in control (B16 cell+PBS) group, 4 died naturally within 55 days, and 2 were killed on the 55th day.All of the 6 mice had metastases in livers, the total number of the melanoma nodes on each liver surface ranged from 2 to 30, with the largest one merging into the whole liver. One mouse had a neoplasm in the remnant site of injection, and 3 had metastases in lungs.In contrast, of the 6 mice in tetrose group, only one died on the 50th day after injection, with 3 metastases in the liver, the largest being 10mm in diameter, the other 5 mice survived until being dissected on the 55th day after injection and had no liver metastasis,but 3 of them had neoplasms in their remnant sites of injection.In mannan group,all of the 6 mice survived and no metastasis was seen except for 2 liver nodes in one mouse with the largest diameter of 1mm.Neither tetrose nor mannan group had metastasis out of the liver, and the weight of liver in the two groups was significantly lower than those in the control group.CONCLUSION:Both tetrose and mannan had the effects of preventing melanoma cells from experimental metastasis to and out of the liver, and prolonging the survival time of the mouse.