The effects of oxygen partial pressure (pO(2)), within the range 10.6-36.5 kPa, on high density cell cultures of Panax notoginseng were investigated in a bioreactor. A pO(2) of 21.3-29.3 kPa was found optimal for the production of cell mass, ginseng saponin and polysaccharide with corresponding values of 24, 1.75 and 3.0 g l(-1) on Day 15, respectively. A low pO(2) was unfavorable to the cell cultures due to oxygen limitation. High pO(2) (36.5 kPa) inhibited cell growth and reduced the production of ginseng saponin and polysaccharide, which was due to the detrimental effect of oxidative burst. The effect Of pO(2) on heterogeneity of ginsenosides produced in the cell cultures was also studied. A high pO(2) (at 36.5 kPa) stimulated Rb-1 biosynthesis in the initial stage of cultivation, while a low pO(2) (at 10.6 kPa) inhibited Rg(1) and Rb-1 formation during cultivation.