Moringa oleifera Lam. is a small tree cultivated throughout India. We have investigated the effect of ethanolic extract of seeds of Moringa oleifera (MOEE, an herbal remedy) on the potential prevention of immune-mediated inflammatory responses in toluene diisocyanate (TDI as antigen)-induced asthma in Wistar rats. Rats were divided into five different groups (n = 8/group): Group-I = unsensitized control; Group-II = TDI control/vehicle; Group-III = dexamethasone (DXM) 2.5 mg/kg; and, Groups IV and V = 100 mg/kg and 200 mg/kg body weight [BW] of MOEE, respectively. All rats (except unsensitized controls) were sensitized by intranasal application of 10% TDI to induce airway hypersensitivity. Animals in Groups II-V were given their respective drug treatment per os from 1 wk prior to initiation of sensitization until the day of final provocation with 5% TDI. After this last challenge, all rats were examined for hyperreactivity symptoms and then sacrificed to determine their total and differential leucocytes in blood and bronchoalveolar (BAL) fluid and levels of TNF proportional, variant, IL-4, and IL-6 in their BAL and serum. Homogenates of one lung lobe from each animal were utilized to assess oxidative stress; a separate lobe underwent histologic examination to assess airway inflammatory status. The results suggest that asthmatic symptoms were found in TDI control rats only, while both MOEE- and DXM-treated rats did not manifest any airway abnormality. In MOEE- and DXM-treated rats, neutrophil and eosinophil levels in the blood were decreased significantly; levels of total cells and each different cell in their BAL fluid were markedly decreased as compared to those in TDI controls. TNF alpha, IL-4, and IL-6 were predominant in serum as well as in BAL fluids in TDI controls, but these levels were reduced significantly by MOEE treatment. The antioxidant activity in relation to antiinflammatory activity of the extract and histopathological observations also reflected a protective effect. Based on the above findings and observations, it can be concluded that Moringa oleifera may possess some beneficial properties that act against chemically stimulated immune-mediated inflammatory responses that are characteristic of asthma in the rat.