Osmotic stress at elevated osmotic pressure was used to stimulate saponin production in Panax ginseng cell cultures. The addition of 0.3 M sorbitol to culture at the time of inoculation, raising the medium osmolality by about 75% (from 150 to 260 mmol/kg), enhanced the saponin accumulation but depressed the cell growth, resulting in no improvement of the volumetric saponin yield of culture. The feeding of sorbitol (0.2-0.3 M, 36.4-54.6 g/L) to culture during the stationary growth phase increased both the saponin content of cell (45-50%) and the volumetric yield (36-38%). With combined feeding of sorbitol (0.2 M) and growth nutrients, sucrose (30 g/L) + casein hydrolysate (0.5 g/L), about 2 days before the stationary phase, the volumetric saponin yield was increased 3.5-fold, 1130.8 mg/L versus the control culture of 251.2 mg/L. Sorbitol in the culture also induced two characteristic stress responses of plant cells, the increase in phenylalanine ammonium-lyase (PAL) activity and the production of reactive oxygen species. This suggests that the stimulated saponin accumulation was part of the cell response to the osmotic stress. (C) 2004 Published by Elsevier Inc.