Panax notoginseng is a commonly used medicinal plant in south-western China. In a previous study, a sequential solubilisation of P. notoginseng high-molecular-weight (HMW) polymers using phenol-acetic acid-water, hot water, weak and strong alkali was performed to determine the structure of the component polysaccharides and proteins. The effects of these extracted HMW fractions on the human complement system, polymorphonuclear neutrophils (PMN) and peripheral blood mononuclear cells (PBMC) are reported here. Fr (1MKOH), which was extracted with 1 M KOH, showed the strongest complement-fixing activity and priming of reactive oxygen species (ROS) production by PMNs, as well as a mitogenic effect. Fr (1MKOH) was further fractionated by anion-exchange chromatography followed by gel-permeation chromatography. 1MD3-G2, the fraction most strongly bound to the DEAE anion-exchange column with a molecular weight of 1140 kDa, showed the highest complement-fixing activity. It is composed of acidic polysaccharides [including glucuronoarabinoxylan (GAX), homogalacturonan (HGA), rhamnogalacturonan I (RG I)], neutral polysaccharides (4-galactan and arabinan), and some protein.