Oral tolerance is a T-cell mediated phenomenon defined by inhibition of immune responsiveness to a protein previously contacted by the oral route. Oral tolerance may prevent autoimmune and allergic diseases that involve the recruitment and/or activation of different cell types including mast cells, neutrophils, eosinophils, monocytes and lymphocytes. The mechanisms by which oral tolerance avoids these immunological disorders are still controversial. Herein we used a murine model of ovalbumin (OVA)-induced peritonitis to investigate the effect of oral tolerance on allergic inflammation. Frequency of leucocyte subpopulations was evalu-ated by global and differential cell counts in peritoneal lavage fluid, per-ipheral blood, and bone marrow. Changes on lymphocyte subsets and adhesion molecules expression by these cells were analysed by flow cyto-metry. As compared with OVA-immune mice, intraperitoneal challenge of tolerant animals with OVA resulted in a significantly milder peritonitis, mostly affecting neutrophils and eosinophils; a concomitant reduction in total white blood cell counts was also observed, mainly because of lower neutrophil and eosinophil counts. Eosinophils, but not neutrophils, were also reduced in the bone-marrow of OVA-challenged tolerant mice. No changes occurred in total peritoneal lymphocyte counts in OVA-tolerant mice, however, there was a significant decrease in CD3 + CD8 + T cells and an increase in B cells (CD45R + ) in these animals as compared to immune OVA-challenged animals. Altered expression of CD18 and CD54, respect-ively, in blood and peritoneal lymphocytes was also noted. These results suggest that, in addition to local specific effects, oral tolerance has sys-temic effects on the mobilization of leucocytes and bone-marrow eosino-poiesis.