A macromolecular fraction from fresh ginseng root containing mainly polysaccharide showed mild mitogenic activity in human cord blood lymphocytes. 2) When lymphocytes were transformed by Con A or PHA, this fraction could greatly enhance the activity of these lectin mitogens, thus showing a potentiation effect. 3) Although this macromolerular fraction contains saponin and is susceptible to trypsin digestion, it is probably a peptido-glycan in nature on account of its important carbohydrate content and thermal stability. 4) This fraction could not support cancer cell (EAT, K562) growth : its inhibitory effect on these cells remains to be explored.