Nigella sativa Linn. (Ranunculaceae) is known to have beneficial effects on a wide range of diseases including asthma. However, the mechanism of action in asthma and other allergic diseases is not entirely clear. The present study was planned to evaluate the effects of Nigella sativa on cytokine production of splenic mononuclear cells in ova-sensitized mice. Nineteen two-month-old BALB/c mice were given 0.3 mL of Nigella sativa oil by oro-eosophageal cannula once a day for a month. The control group consisting of 10 mice took 0.3 mL of 0.9% saline solution by the same route for the same period. In the third week of the study, all mice were sensitized by means of intraperitoneal injections of 20 mu g of ovalbumin (OVA-Grade VI, Sigma). Ova injections were repeated three times with 7-day intervals. After another week, all mice were sacrificed by means of cervical dislocation. Then the splenic mononuclear cells (MNCs) of mice were cultured with OVA or Concavalin A (Con-A). From the culture supernatants, IL-4, IL-10 and IFN-gamma were assessed by means of ELISA. The cytokine production of splenic MNCs of mice that were given Nigella sativa for 30 days was not significantly different than those who took saline solution instead. In conclusion, Nigella sativa oil seems not to have an immunomodulatory effect on Th1 and Th2 cell responsiveness to allergen stimulation. (C) 2005 Elsevier Ireland Ltd. All rights reserved.