The effects of seabuckthorn (Hippophae rhamnoides L., Elaeagnaceae), leaf aqueous extract were examined in rats for its adaptogenic activity and toxicity. Dose dependent adaptogenic study of extract was carried out at different doses administered orally, 30min prior to cold (5 degrees C)-hypoxia (428mmHg)-restraint (C-H-R) exposure. After sub-acute toxicity studies on 10 and 20 times doses of maximal effective dose administered for 14 days (single oral dose of 1g/kg and 2g/kg once daily) and maximal effective dose administered for 30 days (single oral dose of 100mg/kg once daily), biochemical and hematological parameters were studied in the serum and blood. The maximal effective adaptogenic dose of the extract was 100mg/kg body weight. No significant changes were observed in organ weight/body weight ratios, of any vital organ studied (except liver and kidney in 1g/kg and 2g/kg body weight doses, respectively), and biochemical and hematological parameters of the sub-acute drug treated animals in comparison to control rats. In acute toxicity study LD(50) of the extract was observed to be >10g/kg when given orally. These results indicate that seabuckthorn leaf aqueous extract possess potent adaptogenic activity with no toxicity even after sub-acute (30 days) maximal effective dose administration.