To examine the effect of Aged Garlic Extract (AGE) on the function of mast cells and activated T lymphocytes, we adopted the in vitro histamine release system, the in vivo IgE mediated skin reaction system and the in vivo late phase reaction system. Consequently, at 1.25, 2.5, and 5.0% (v/v), AGE dose-dependantly inhibited the antigen specific histamine release by mouse anti-TNP monoclonal antibody and TNP-BSA hapten carrier complex against rat basophil cell line RBL-2H3 by 50, 80, and 90 percent, respectively. In the IgE mediated skin reaction system, repeated or single intragastric administration of AGE (10 ml/kg), decreased by 25-45% the antigen specific ear swelling which was induced by a picryl chloride ointment applied to the ear of mice also given an intravenous administration of anti-TNP antibody IgE ascites. In the late phase reaction system, repeated or single intragastric administration of AGE (10 ml/kg) suppressed by 45-55% the antigen specific ear swelling induced by a secondary challenge to the ear of mice given a picryl chloride ointment seven days prior. These results suggest that AGE application could modify, directly or indirectly, the function of mast cells, basophils and activated T lymphocytes which play a leading role in allergic cascade reactions including inflammation.