The aqueous suspension of root extract of an Indian drug ashwagandha (Withania somnifera L. (Solanaceae)) was evaluated for its effect on lipid peroxidation (LPO) in stress-induced animals. Elevation of LPO was observed in rabbits and mice after intravenous administration of 0.2 microg/kg of lipopolysaccharide (LPS: from Klebsiella pneumoniae) and 100 microg/kg of peptidoglycan (PGN: from Staphylococcus aureus), respectively. The peak was reached immediately after PGN and 2-6 h after LPS administration. Simultaneous oral administration of ashwagandha (100 mg/kg) prevented the rise in LPO in rabbits and mice.