We studied the effect of aqueous extract of Kum-Hwang-San (KHS) on mast cell-mediated immediate type allergic reactions. KHS (1-100 microg/site) inhibited concentration-dependently mast cell-dependent ear swelling response induced by compound 48/80 (200 microg/site) in mice by both topical and intradermal application. KHS (0.1-100 microg/site) inhibited concentration-dependently passive cutaneous anaphylaxis induced by anti-dinitrophenyl (DNP) IgE in rats by both topical and intradermal application. KHS also inhibited concentration-dependently the histamine release from the rat peritoneal mast cells (RPMC) by compound 48/80 and anti-DNP IgE. Moreover, KHS had a significant inhibitory effect on anti-DNP IgE-induced tumor necrosis factor-alpha (TNF-alpha) secretion from RPMC. These results indicate that KHS inhibits immediate type allergic reactions by inhibition of histamine release and TNF-alpha secretion from mast cells in vivo and in vitro.