We studied the effects of lavender oil on mast cell-mediated immediate-type allergic reactions in mice and rats. Lavender oil (1:500, 1:100, 1:10, 1:1, 1:0) inhibited concentration-dependently mast cell-dependent ear swelling response induced by compound 48/80 in mice by both topical and intradermal application. Lavender oil (1:500, 1:100, 1:10, 1:1, 1:0) inhibited concentration-dependently passive cutaneous anaphylaxis induced by anti-dinitrophenyl (DNP) IgE in rats by both topical and intradermal application. Lavender oil (1:500, 1:100, 1:10, 1:1, 1:0) also inhibited concentration-dependently the histamine release from the peritoneal mast cells by compound 48/80 or anti-DNP IgE. Moreover, lavender oil (1:1000, 1:100, 1:10, 1:0) had a significant inhibitory effect on anti-DNP IgE-induced tumour necrosis factor-alpha secretion from peritoneal mast cells. These results indicate that lavender oil inhibits immediate-type allergic reactions by inhibition of mast cell degranulation in-vivo and in-vitro.