The effect of initial sucrose concentration was investigated in embryogenic cell cultures of Eleutherococcus sessiliflorus in bioreactors for production of eleutherosides, phenol, flavonoids and polysaccharide. The final dry cell weight was increased from 6.16 to 23.33 gl(-1) with an increase of initial sucrose concentration from 10 to 70 gl(-1), but an even higher sucrose concentration of 90 gl(-1) seemed to repress the cell growth. Furthermore, it was found that a high sugar level was favorable to the synthesis of eleutherosides, phenol and flavonoids, which may be due to higher osmotic pressure. A marked increase in malondialdehyde (MDA) content in germinating embryos was observed in high sucrose treatment. MDA, a decomposition product of polyunsaturated fatty acids hydroperoxides, has been utilized very often as a suitable biomarker for lipid peroxidation, which is an effect of osmotic stress. This hypothesis is also confirmed by the higher lipoxygenase (LOX) activity under this treatment. The much higher antioxidant enzyme activities in the culture fed with higher initial sucrose suggest that osmotic stress arising from a sudden increase in medium osmotic pressure. A hypothesis of osmotic stress and eleutheroside accumulation was confirmed from these results. (c) 2005 Elsevier Ltd. All rights reserved.