The suspension and the boiling water extract of dried powder from the aerial parts of Bidens pilosa L. var. radiata SCHERFF (Tachiawayukisendangusa: MMBP) on the Japanese island of Miyako have antiinflammatory and antiallergic properties in experimental diseases. Oral administration of MMBP suspension in carboxy-methyl-cellulose sodium solution inhibited the production of IgE 10 days after immunization with DNP-ascaris in mice. The extract inhibited histamine release from rat peritoneal mast cells induced by compound 48/80 or antigen-antibody reaction. Oral administration of the suspension inhibited dye exudation in rat skin induced by passive cutaneous anaphylaxis. Oral administration of the suspension inhibited dye exudation in rat skin induced by chemical mediators (histamine, substance P, and serotonin). These findings suggest that MMBP may be clinically useful in the prevention of type I allergic disease.