The present study evaluated the immunomodulatory effects of chelidonic acid, a secondary plant metabolite, with therapeutic potential in allergic disorders, in experimental animals. In mast cell degranulation studies, ovalbumin immunized and challenged rats, chelidonic acid (1, 3 and 10 mg/kg, i.p.) dose relatedly prevented ovalbumin challenge induced mast cell degranulation by differing degrees when compared with vehicle treated group, and these effects were comparable with prednisolone (10 mg/kg). A reduction in post-challenge mortality was also observed in all treated groups. Further, there were reductions in the blood eosinophil counts and serum IgE levels after chelidonic acid treatment. Chelidonic acid also inhibited histamine release from rat peritoneal mast cells (RPMC) in vitro, in a dose related manner. In tests for adaptive immunity, in rats immunized with sheep RBC, chelidonic acid differentially suppressed the (a) plaque forming cell (PFC) count in rat splenic cells, (b) anti-SRBC antibody titre and serum IgG levels and (c) increases in foot pad thickness in the DTH assay — all of which were comparable with prednisolone. These experimental results are discussed in light of the possible therapeutic potential of chelidonic acid in allergic disorders.